Canadians "have an important choice to make" about their country's future path, Liberal Leader Justin Trudeau said today as he triggered the official launch of the federal election campaign.

Trudeau and his wife Sophie Grégoire Trudeau arrived at Rideau Hall in Ottawa this morning to ask Gov. Gen. Julie Payette to dissolve Parliament, launching Canada's 43rd general election.The vote is to be held on Oct. 21.

Dogged by new questions about the SNC-Lavalin scandal, Trudeau — who is seeking his second four-year mandate — wasted little time in posing what the Liberals hope will be the ballot box question.

"We've done a lot together these past four years, but the truth is, we're just getting started. So Canadians have an important choice to make. Will we go back to the failed policies of the past, or will we continue to move forward?" Trudeau told reporters outside Rideau Hall.

"That's the choice. It's that clear. And it's that important. I'm for moving forward for everyone."

Watch: Trudeau kicks off election campaign

Liberal leader Justin Trudeau arrived at Rideau Hall in Ottawa this morning to ask Gov. Gen. Julie Payette to dissolve Parliament, and launching 43rd general election campaign. 0:49

Trudeau's Liberals will spend the next 40 days pitching Canadians on the party's accomplishments — especially their efforts to lift children out of poverty and create jobs — while trying to contrast themselves on social issues with their main rivals.

They'll also be working to distance themselves from the lingering SNC-Lavalin scandal, which re-emerged just hours before the election call.

Late Tuesday the Globe and Mail reported that the RCMP's probe into potential obstruction of justice in the SNC-Lavalin affair has been hindered because the federal government won't lift cabinet confidentiality for all witnesses.

The probe was the subject of the first question put to Trudeau at the media availability in Ottawa.

"We gave out the largest and most expansive waiver of cabinet confidence in Canada's history," Trudeau replied, referring to the waiver his office gave former attorney general Jody Wilson-Raybould earlier this year allowing her to disclose some details of her conversations with government officials about the prosecution of SNC-Lavalin, a Montreal-based global engineering and construction company.

"We respect the decisions made by our professional public servants. We respect the decisions made by the clerk."

A Liberal campaign spokesperson said that, as of today, the national police force has not contacted any current or former PMO staff for documents or interviews related to the SNC Lavalin affair. The RCMP would not comment on the Globe story.

Watch: Trudeau responds to questions over SNC-Lavalin affair

Liberal Leader Justin Trudeau said he respects the decision the Privy Council Clerk made over the SNC-Lavalin affair during a news conference at Rideau Hall Wednesday. 0:27

Trudeau side-stepped questions about whether he thinks he made any personal mistakes related to the SNC-Lavalin file.

"My job as prime minister is to be there to stand up for and defend Canadians' jobs," he said.

Conservative Leader Andrew Scheer, starting his first general election campaign as leader, jumped on the headline today, taking media questions at the Ottawa airport ahead of Trudeau's stop at Rideau Hall.

The Conservatives plan to go after aspects of the government's record — especially Trudeau's ethics breach in the SNC-Lavalin affair — while promising to ease Canadians' economic anxieties.

Watch: Canadians can't trust Trudeau, Scheer says

Conservative Leader Andrew Scheer said the SNC-Lavalin affairs shows Canadians "just cannot trust Justin Trudeau," while answering questions before the Trudeau called the federal election Wednesday. 0:41

Last month, Ethics Commissioner Mario Dion found Trudeau violated the Conflict of Interest Act by trying to urge Wilson-Raybould to overrule a decision denying a deferred prosecution agreement to Quebec-based engineering firm SNC-Lavalin.

"He has lost the moral authority to govern," Scheer said. "What today shows is you just cannot trust Justin Trudeau."

Polls show a tie

According to CBC's Canada Poll Tracker, an aggregation of all publicly available polling data, the Conservatives and Liberals are now deadlocked, after the Tories had enjoyed a lead stretching back to February and the start of the SNC-Lavalin affair.

The Liberals are at this moment projected to win the most seats — but whether any party can secure a majority after the 40-day campaign remains to be seen.

That makes the fight for third place especially interesting to watch.

The NDP, which is fighting against sinking polling figures and a diminished war chest, is trying to pitch itself as a viable alternative to the two front-runners and appeal to progressive voters embittered by the Liberals' last four years in office.

The leaders of Canada's main political parties, clockwise from top left: NDP's Jagmeet Singh, Liberal Party's Justin Trudeau, Conservative Party's Andrew Scheer, Yves-Francois Blanchet of the Bloc Québécois, Green Party's Elizabeth May, and People's Party of Canada's Maxime Bernier. (Ben Nelms/Reuters, Henry Nicholls/Reuters, Chris Wattie/Reuters, Justin Tang/The Canadian Press)

"We're looking at what's going on right now in Canada and what I'm hearing from people is that they're done with governments that seem to prioritize making it easier for the very rich and harder for them," said NDP Leader Jagmeet Singh while kicking off his first campaign as party leader in London, Ont.

"I'm confident people will see in us champions who want to put them at the centre and heart of everything we do."

Nipping at the NDP's heels in the polls are the Greens. Leader Elizabeth May launched her campaign in British Columbia, a region where her party hopes to make a breakthrough to build on her party's current two-seat caucus in the House of Commons.

"This is the most important election in Canadian history," May told a room full of supporters in Victoria.

"This election is about telling the truth to Canadians about how serious the climate emergency really is. And we do that in order not to create fear, we do that in order to give everyone hope. We have a plan."

Former Conservative Maxime Bernier is hoping to make a splash with his new party, the People's Party of Canada (PPC), by holding on to his own seat and bringing new MPs to Parliament. On election kick-off day, the PPC was polling around four per cent.

While promising to run a campaign to "put Canadians first," he underscored one of the biggest problems facing his party: getting him on a debate stage.

(CBC News)

After initially being turned down, Bernier is still waiting to find out if he'll be invited to the English and French language debates being organized by the Leaders' Debates Commission, which was established after the last election and is led by former governor general David Johnston.

After dismantling itself, replacing its leader and then coming together again, the Bloc Québécois will be looking to win at least 12 seats in Quebec and regain official party status — a title it hasn't held since 2011.

Bloc Leader Yves-François Blanchet, whose party is also polling around four per cent, spoke to supporters today in Quebec City, urging Quebecers to think of where they want to go "not as a province, but as a nation."

Conservative Leader Andrew Scheer kicked off the election campaign in Quebec where he was asked about the controversial Bill 21. 0:50

Secularism bill emerges day 1

The main parties are fanning out across the country today by plane and bus, hitting the regions they see as key to victory.

While the Liberals and Tories are tied nationally, the way their support breaks down regionally could lead to quite different results on election day.

Scheer's Conservatives hold a daunting lead in Alberta, Saskatchewan and Manitoba and are hoping to steal seats in Quebec.

Scheer started his campaign today in Trois-Rivieres, Que., a seat in the heartland between Montreal and Quebec City, tearing into both Trudeau and the Bloc. He'll finish the day with a rally in Woodbridge, Ont., a suburb of Toronto

'You and your family are at the heart of the October 21st election," said Conservative Leader Andrew Scheer. 0:46

The Liberals lead by six points in Ontario and 14 points in Quebec, which could deliver around 121 seats at this point, according to the Canada Poll Tracker.

Quebec-focused issues surfaced on day one of the campaign, with Trudeau and Scheer both fielding questions about that province's secularism bill, known as Bill C-21, which bans the display of religious symbols and clothing by teachers, judges, police officers and other public sector workers.

Watch: Scheer says Conservatives won't intervene in Quebec's Bill 21

'We are going to bring a hopeful message to Canadians that we can build the country of our dreams," says NDP Leader Jagmeet Singh. 0:44

"I said many times, I am deeply opposed to Bill 21 in Quebec. I don't think that, in a free society, we should be legitimizing or allowing discrimination against anyone," said Trudeau when asked if his government would challenge the law.

"We are following very carefully the process. At this time, we feel it would be counterproductive for the federal government to engage in the process with which Quebecers are underway, but we will continue to monitor closely and evaluate our position."

Scheer said the law is not something a Conservative government would ever consider at the federal level.

"We will always stand up for the rights of Canadians and the rights for expression and the rights of freedom of religion," he said.

Trudeau is heading to British Columbia to hold a rally tonight in the riding of Vancouver Kingsway, a seat held by New Democrat Don Davies for the past decade.

'This is the most important election in Canadian history," says Green Party Leader Elizabeth May. 0:48

While today's visit to Rideau Hall marks the official launch of the campaign, the parties have been stumping all summer, airing TV and digital ads, circulating their campaign slogans and unearthing nuggets of opposition research.

The start of the writ period isn't just ceremonial. As of today, strict rules kick in on spending and advertising.

Trudeau, Scheer, Singh, May and Blanchet all started their speeches by reflecting on the anniversary of the Sept. 11 terrorist attacks.