OTTAWA — Two of the four leaders set to face off tonight in the first televised debate of the federal election campaign went out ahead of the event to drum up support.

The French debate on TVA, one of Quebec's most-watched networks, comes at the mid-point of the campaign and could prove crucial to the outcome on Sept. 20.

Only four leaders — the Liberals' Justin Trudeau, the Conservatives' Erin O'Toole, the Bloc Québécois' Yves-Francois Blanchet and the NDP's Jagmeet Singh — will take part.

The Green party's Annamie Paul and the Peoples' party's Maxime Bernier were not invited to participate.

The TVA debate was seen as pivotal in the 2019 campaign.

Then-Conservative leader Andrew Scheer's evasiveness on the issues of abortion and medical assistance in dying was widely seen as halting early Conservative momentum, ultimately enabling Trudeau's Liberals to eke out a minority win.

The performance of Blanchet, a newcomer to federal politics at the time, was also credited with giving new life to the Bloc Québécois, which helped rob Trudeau of a second majority mandate.

Blanchet and O'Toole had no public events in the hours leading up to their debate, which will also be a first for O'Toole as Conservative leader.

Trudeau hit Montreal's Saint Laurent Boulevard around lunchtime, stopping to chat and pose for countless photos with students in frosh week shirts, shop owners and young families with babies in tow.

He stopped at one point to buy smoked meat sandwiches for his team and latkes for himself. A worker from another business came out to give Trudeau Portuguese custard tarts.

Four leaders square off in first televised #debate of federal election campaign. #ItsOurVote #CdnPoli #Elxn44

Trudeau — who was flanked by six candidates, including cabinet ministers Steven Guilbeault and Melanie Joly — encountered a largely friendly crowd on Thursday. He was heckled once by a passerby and again by two patrons on a restaurant patio.

Singh handed out samples of his personal recipe for "Punjabi poutine" from a custom truck that almost didn't make it after a wheel fell off — something the New Democrats hope doesn't happen to their campaign in Quebec.

The province in 2011 helped make the NDP the Official Opposition, but in 2019 they lost all but one seat there.

The NDP leader told reporters that his strategy going into the debate was to target Trudeau and the Liberal government's policies and paint a stark choice for voters.

"They can choose another four years of Justin Trudeau, who has made all the things that people care about in Quebec worse — the housing crisis, environmental crisis, those have become worse with Justin Trudeau — or they can choose New Democrats, who have shown that we fought for them," Singh said.

"And we will continue to fight for them, and we'll make sure that we solve the problems that people need solving."

The TVA debate is in addition to two official debates organized by the Leaders' Debates Commission. The official debates are scheduled to take place next week — in French on Sept. 8 and in English on Sept. 9.

Paul will participate in those debates, but Bernier, who didn't meet the independent commission's criteria for participation, will not.

The TVA debate involves a series of face-to-face encounters between two leaders at a time, allowing for sharper and longer exchanges.

Tonight's two-hour debate begins at 8 p.m. ET.

- With files from Paola Loriggio