Liberal Leader Justin Trudeau took aim at the Conservatives on Sunday for not releasing their election platform as the majority of federal party leaders spent the day cramming for Monday's critical English-language debate.

The debate is in Gatineau, Que., within sight of Parliament Hill. Trudeau and NDP Leader Jagmeet Singh were the only two leaders to spend the day on the hustings, shaking hands and, in Trudeau's case, attacking the Tories, though neither strayed far.

Conservative Leader Andrew Scheer and Green Leader Elizabeth May were either in or en route to Ottawa to prepare for Monday night's televised debate, arguably the most important event of the campaign so far.

Bloc Quebecois Leader Yves-Francois Blanchet and People's Party of Canada Leader Maxime Bernier are also taking part, the first time all six leaders will square off on the same stage.

Monday's debate is also the last time any of them will debate each other in English.

Trudeau made a quick bus trip to a conservative-friendly area just outside Belleville, Ont., where he planted trees to highlight his environmental plan, including a promise to plan two billion trees.

Compared Scheer to Ford

He then went on the offensive, attacking Scheer for promising to cancel the Liberals' price on carbon before comparing the Tories' refusal to release their platform to that of Ontario Premier Doug Ford.

"I can talk about what's in our platform because we have released our full platform," said Trudeau, whose party and the Greens have released cost estimates for most promises and how they intend to pay for them.

Conservative Leader Andrew Scheer arrives for the TVA french language debate in Montreal last week. The leaders will spend most of Sunday evening and Monday preparing for Monday night's English debate. (Ryan Remiorz/The Canadian Press)

"Andrew Scheer is keeping his full platform and its costing a secret. You know who else did that? Doug Ford. He kept it secret from Canadians and then turned around and cut health care, cut education, cut services for people who need it."

After promising a fully costed platform, Ford's Progressive Conservatives instead released a list of promises about a week before Ontarians went to the polls in June 2018. The list did not include details on how the PCs would pay for the promises.

Upon taking office, the Ford government — a constant target for Trudeau — moved to cut funding for public-health services, new child-care spaces and autism support. It also announced increases to class sizes, among other things.

Platform coming: Scheer

Scheer has refused to be pinned down on the timing of the Conservative platform release, saying only that it will be unveiled "with plenty of time for Canadians to make decisions, to go through it."

Tory spokesman Simon Jefferies said Sunday that the party platform will be fully costed when it's released and that some of the Liberals' signature promises don't have dollar figures attached.

The NDP released their platform in June, several months before the election was even called. However, Singh has not yet released a costing of the platform or a fiscal plan. A party spokesman has said these are coming.

The People's Party of Canada has similarly announced some tax measures, but not year-by-year fiscal estimates.

Even as Trudeau was attacking the Conservatives on Sunday, Singh was enlisting one of his party's most respected elder statesmen, Ed Broadbent, for a tour of an Ottawa farmers market.

The market is in Ottawa Centre, which Broadbent represented in his short, second stint in politics from 2004 to 2006. Liberal Catherine McKenna won it from Broadbent's NDP successor Paul Dewar in 2015 and the New Democrats would like to take it back.

Tour with Broadbent

Under grey skies, Singh and Broadbent, who led the federal New Democrats from 1975 to 1989 and remains a force within the party even at age 83, shook hands with marketgoers who were eager for selfies with the two men.

Broadbent praised Singh for his performance during last week's French-language debate. Asked what advice he would give Singh ahead of Monday's English-language debate, Broadbent responded: "To be himself."

Former NDP leader Ed Broadbent listens to current leader Jagmeet Singh as they tour a farmers market in Ottawa on Sunday. (Paul Chiasson/The Canadian Press)

Singh, who at times seem to be more readily recognized by shoppers than Broadbent, described the former leader as "a great mentor," and that when it comes to the debate: "I'm going to try my best."

At one point during his tour, Singh was approached and thanked by one shopper for his response to photos and a video of Trudeau having worn blackface and brownface makeup before the Liberal leader entered politics.

"As a person of colour, I was inspired and grateful for how his response was to Justin Trudeau," said Laverne Barretto. "It spoke to my heart and to my soul and his poise and elegance was profound. ... That really meant a lot to me as a woman of colour in Canada and I really wanted to say thank you."

Yet Barretto said she would be voting for the Greens because she wants to push for more action on the environment and climate change and that it was unfortunate the NDP's platform did not go farther.

Kenney has advice

The NDP leader wasn't the only one getting some advice ahead of Monday's debate. Alberta Premier Jason Kenney, who was in Ottawa last week campaigning on behalf of Scheer, said the Conservative leader needs to avoid becoming defensive.

Scheer emerged as the main target for the other leaders during last week's TVA French-language debate.

"He'll be under attack because I think he's leading in this campaign," Kenney said Friday. "So my advice to him would be: Don't become too defensive. Get out there, communicate your message. That's what I did and it worked for us."

In a fundraising letter to supporters, Bernier described Monday's debate and the French-language debate that will be held on Thursday as a potential "turning point" in the campaign. Bernier has been betting that a chance to speak to a national audience will give him a critical boost.

"Millions of Canadians will be hearing about the People's Party for the first time," said Bernier, who was excluded from the first English-language debate held last month by Maclean's and Citytv as well as the TVA debate.