TORONTO — The leaders of Ontario's three main political parties will square off on the same stage for the first time Monday, just days before the official start of the province's spring election campaign.

Liberal Premier Kathleen Wynne, Progressive Conservative Leader Doug Ford and New Democratic Party Leader Andrea Horwath will all participate in the live debate in Toronto, which will be broadcast on City TV.

It's the first of three debates scheduled before the June 7 vote and observers say it will give voters a clear view of how the parties and their leaders intend to campaign once the writ drops two days later.

"The (party) strategists have had several months to think about how to package their appeals, which voters they want to collect to their side and how to try to depict the opposition's limitations against their own virtues," said Cristine de Clercy, an associate political science professor at Western University. "We'll see a small template of their messaging."

Many will be watching Ford closely as the new Tory leader debates two seasoned provincial politicians, de Clercy said.

"It's worth remembering he just got this job," she said. "For him it's a test of leadership, does he have the gravitas, control and focus to show what he'll do as premier?"

The debate will also begin to draw increased scrutiny to the campaign, which has unofficially been underway for weeks, de Clery said.

That means issues like Ford's recent flip-flop on whether to allow development in a large protected green space around the Toronto region — first pledging he would, then reversing course — will take on added importance, she said.

"If Mr. Ford continues to take positions that he has to very hastily back away from ... he will not look credible or trustworthy on policy. That, for him, is a big liability."

And on Saturday, the Tory leader removed Tanya Granic Allen, a social conservative and outspoken opponent of the province's sex education curriculum, from the PC ballot in Mississauga Centre.

Granic Allen's dismissal came hours after the Liberals shared an edited video in which she expresses views the governing party described as representing "hatred and homophobia."

Horwath, meanwhile, has to make an impact with voters during the debate, parlaying her high personal approval ratings into support for the NDP brand, which lags in the polls, de Clercy said.

Horwath has led the NDP since 2009, but failed to move it beyond third-party status during her tenure so far.

"The challenge for Ms. Horwath is to communicate that she is a credible alternative," de Clercy said. "She has many virtues as a politician, but her single biggest liability is her party and its history in Ontario."

For Wynne, whose Liberals have held power for 15 years, the focus will likely be Ford, said Nelson Wiseman, a political-science professor at the University of Toronto.

The premier will use her attacks to further contrast her approach to running the province with Ford's plans, said Wiseman.

"Wynne is going to be tearing strips off Ford," he said, adding that the Liberal leader would likely try to associate Ford with his late brother Rob Ford, the infamous former mayor of Toronto, as well as U.S. President Donald Trump.

The fiery Doug Ford, a former Toronto city councillor who has lambasted the Liberals for their spending, will have to hold up under the pressure and remain in control of his emotions, Wiseman said.

"He's got to try not to appear wild, like his brother," he said. "He's already demonstrated some of that in the campaign."

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Wiseman said while people tend to think the impact of debates are immediate, research shows they often help voters form opinions in the longer-term.

He points to the first debate of the last federal election that helped Justin Trudeau establish himself and the Liberals as a viable alternative to Stephen Harper's Conservatives, starting a shift that saw support bleed from the NDP to Liberals.

A similar dynamic could be at play in Ontario, Wiseman said, with polls pointing to voters wanting a change in government but many being undecided on who to get behind — the Tories or the NDP.