TORONTO -- As leaders of the six main federal parties prepare to square off in Thursday night’s French-language debate, the last one before voters head to the polls on Oct. 21, political commentators say their performances could have a big impact not only on the battle for Quebec, but the final balance of power.

Liberal Leader Justin Trudeau, Conservative Leader Andrew Scheer, NDP Leader Jagmeet Singh, Green Party Leader Elizabeth May, Bloc Quebecois Leader Yves-Francois Blanchet, and People’s Party of Canada Leader Maxime Bernier will take to the stage before a live audience at the Canadian Museum of History in Gatineau, Que. for a two-hour debate at 8 p.m. ET.

While there is expected to be some overlap in terms of topics that were discussed during Monday night’s English-language debate, two new umbrella categories--“identity, ethics and governance” and “services to seniors”--as well as a slightly different format is likely to shake things up.

Not to mention the fact that the entire debate will be exclusively in French, a fact that CTV News political commentator Tom Mulcair says will provide an extra challenge for Scheer. He said the Conservative leader struggled with the language during last week’s TVA debate, which hurt his party’s chances in Quebec.

“They’re going to have to try and figure out which Andrew Scheer shows up,” Mulcair told CTV News Channel on Thursday. “Is it going to be the tough, well-organized, well-prepared Andrew Scheer who was there for the English debate on Monday or is he going to try to muddle through as he did last week? That could be disastrous for the Conservatives.”

Mulcair said Scheer’s poor showing at last week’s debate gave Blanchet a boost in the province.

“The Bloc Quebecois is now dominant in those regions where the Conservatives had hoped to break through,” he explained.

Stewart Prest, a political science lecturer at Simon Fraser University in B.C., said the Bloc Quebecois’ resurgence means there will be additional pressure on Blanchet to do well at Thursday’s debate. He said the leader will enjoy certain advantages over his rivals, such as his command of the language and the fact that he’s only trying to appeal to Quebec voters.

“It’s going to be really fascinating to see,” Prest told CTV News Channel on Thursday. “He has to nail the performance here to solidify those gains they’ve made over the last couple of weeks.”

It won’t be all smooth sailing for Blanchet, Mulcair cautioned. He said the leader will likely be in the hot seat tonight after news broke earlier this week that four Bloc Quebecois candidates had posted anti-Islamic messages and videos on their social media accounts.

“He’s going to have some explaining to do tonight,” Mulcair predicted. “Up until now, the first couple of debates, it’s just been a free game for him. He’s been on the attack and there’s been no comeback against him. That’s about to change tonight. We’ll see if it will really make a difference.”

Blanchet already apologized for the candidates’ “inappropriate” social media posts in a statement released earlier on Thursday.

“I have personally spoken to each of these candidates,” Blanchet said. “They all regret having in the past shared videos or messages containing inappropriate remarks. They apologize. And as the leader of the Bloc Quebecois, I also apologize on their behalf to all Quebecers.”

Bill 21

Prest said Trudeau is Blanchet’s main challenger for Quebec’s seats and he will have to pull off a delicate “balancing act” at the debate when it comes to the topic of Bill 21. The Liberal leader has vowed to leave the door open to a possible federal intervention in the provincial law, which bans civil servants from wearing religious symbols, such as a turban, while on the job.

“[He’s] trying to support the idea of a diverse Canada and respect for human rights and leaving a door open, as he calls it, to challenging Bill 21 and yet not being so forceful on that statement that he starts to alienate some of those Quebecers who are currently thinking of voting for the Liberals,” he said.

Blanchet, on the other hand, has been staunchly in favour of the secularism bill, which has received widespread support in Quebec.

“It’s really just going to play out in that competition for who comes up as the first and second place in Quebec,” Prest said.

Mulcair said he wouldn’t be surprised if Trudeau goes “all in” on his opposition to Bill 21.

“He’s already going to lose the seats he’s going to lose in Quebec so he might make a big play on individual rights that will go straight to the hearts of people in greater Vancouver, in Greater Toronto,” he said. “If he uses the Bloc Quebecois’ resurgence as a threat in the rest of Canada, saying ‘You can’t give these guys the balance of power,’ it might just work for him.”

As for the other party leaders, they’ll have their work cut out for them if they want to win over voters in the province with the second-highest number of seats, after Ontario.

“It’s a heck of race here in the province of Quebec,” Mulcair said. “I’ve said for some time that the massive number of seats in Ontario will of course be determinant with regard to who wins the election, but whether that winner gets a minority or a majority will really rely on the 78 seats here in Quebec.”

According to the latest national tracking numbers from Nanos Research, the Liberals are still in the lead with 37 per cent support followed by the Conservatives at 33 and the NDP at 14 per cent. The Greens continue to trail behind in fourth place with 8 per cent support while the Bloc Quebecois have 5 per cent and the PPC have 1 per cent.

Methodology

The Nightly Nanos Election Tracking is produced by Nanos Research, CTV News and the Globe and Mail. The data is based on dual frame (land + cell-lines) random telephone interviews using live agents of 1,200 Canadians using a three night rolling average of 400 respondents each evening, 18 years of age and over.

The random sample of 1,200 respondents may be weighted by age and gender using the latest census information for Canada. The interviews are compiled into a three night rolling average of 1,200 interviews, where each evening the oldest group of 400 interviews is dropped and a new group of 400 interviews is added.

A random telephone survey of 1,200 Canadians is accurate ±2.8 percentage points, plus or minus, 19 times out of 20.