Tonight's French-language debate may not get the same attention outside Quebec as the previous debates, but it could still prove influential on the outcome of the election.
"This debate matters, because if there's ever a shot at breaking the NDP stranglehold on Quebec voter love right now, this is it," said David McLaughlin, the former chief of staff to Brian Mulroney. "If the NDP loses ground in Quebec, then there's no way they can form a minority government."
The NDP continues to lead in the polls in the province, where it held 53 seats before the dissolution of Parliament, followed by the Liberals with seven, the Conservatives with five and the Bloc Québécois with two.
Here are five things to watch for in the debate, the first to feature all five party leaders:
1. Enter Gilles Duceppe
This will be the first time in the campaign the Bloc leader has participated in a leaders' debate, and with his party on political life-support, it could be his last chance to make a major splash in the province. With nothing to lose, and as the head of a party with only two members of Parliament, expect Duceppe to come out swinging.
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How to watch Thursday's debate
The French-language leaders' debate will be broadcast live and live streamed online 8 p.m. to 10 p.m. ET Thursday.
You can watch the debate in simultaneous English translation on CBC News Network and online at CBCNews.ca/Canada Votes beginning with a Power & Politics pre-debate special at 7 p.m. ET. The debate will be broadcast in French by Radio-Canada (check local listings) and live streamed online at ICI Radio-Canada.ca.
The debate is being produced by a partnership of Radio-Canada, La Presse, Télé-Québec, CBC News, CTV News and Global News, together with Facebook, Instagram, Twitter, Vine, Google, YouTube and CPAC.
2. The Mulcair/Duceppe show
And who exactly will Duceppe be swinging at? One would normally think the prime minister would be the focus of any kind of debate. But tonight, Conservative Leader Stephen Harper may just stand back, try to look prime ministerial, and watch the others attack the main target — NDP Leader Tom Mulcair.
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Liberal Leader Justin Trudeau will try to get in his shots, said Christian Bourque, executive vice-president of Léger Marketing. "I think the Mulcair/Duceppe duel will be the main feature of the debate."
All the leaders will take turns aiming shots at Mulcair, but expect Duceppe to be the most aggressive, challenging Mulcair on a number of issues including the niqab, daycare and pipelines.
3. Speaking of the niqab
It's one of those hot-button wedge issues — whether a woman should have the right to wear a niqab while taking the oath of citizenship — but it's still unclear what influence it will have on voting decisions. Still, Duceppe has come out strongly against it, saying he'd be in favour of invoking the notwithstanding clause in the Charter of Rights and Freedoms to ban the wearing of a niqab during the oath.
"Why Gilles Duceppe will want to use that against Tom Mulcair in [tonight's] debate is basically because it makes the NDP look to be in contradiction with what the Bloc would say is the will of Quebecers," said Bourque.
In a speech in Montreal on Wednesday, the day before the debate, Mulcair clarified his stand, saying he supports the current requirement that women show their faces at some point in the citizenship process but that they should not be forced to remove a face covering while taking the oath of citizenship.
"If you are Tom Mulcair, you want this not to be the main focus of the debate. So by giving out what his position is, and clearly stating what his position is … he'll be able to say, 'I've said it clearly, here's how I feel about it, I've said it yesterday, there's no more to add."
4. Energy East pipeline
The proposed 4,600-kilometre pipeline would carry 1.1-million barrels a day of oilsands crude from Western Canada to refineries in Quebec and New Brunswick. But it's become a controversial issue in the province, with concerns that the pipeline carries ecological risks. It was talked about briefly in the first debate, where Trudeau accused Mulcair of flip-flopping, while Harper accused Trudeau of the same.
This time, Duceppe, who opposes the plan, gets to weigh in, and he will likely focus on Mulcair, accusing him of supporting the pipeline when speaking to the West, but opposing it when in Quebec. Mulcair has said the pipeline should not be approved without a thorough and credible environmental evaluation, but that the notion of bringing oil from West to East could "accomplish a lot of positive things."
5. Policy plugs
As with the last debates, expect all leaders to plug policies they think would play well for a Quebec audience. For example, Trudeau may talk about scrapping the plan to buy F-35 fighter jets and his announcement this week to boost spending for the arts. Harper might remind viewers that his government would make Quebec's Collège Militaire Royal de Saint-Jean a degree-granting military university. Meanwhile, Mulcair will boast that his national daycare plan is patterned after Quebec's.