NDP Leader Tom Mulcair and Liberal Leader Justin Trudeau have confirmed their participation in a leaders' debate on foreign issues despite having raised concerns about the event's bilingual format.

Their participation in the Munk Debates means that Canadians will have the opportunity to see where the three main party leaders stand on foreign policy.

The Conservatives had already confirmed that Stephen Harper would take part in the debate, scheduled for Sept. 28 at Roy Thomson Hall in Toronto.

Rudyard Griffiths, the moderator and chair of the Munk Debates, said on Monday the event would be broadcast in both official languages online and on the Canadian Public Affairs Channel (CPAC), and that the leaders could use the language of their preference at any time during the debate.

Mulcair, Trudeau in but concerns remain

That appeared to satisfy both Mulcair and Trudeau who in recent days had raised questions about whether the debate would be bilingual enough to satisfy their conditions for equal French and English debates. The NDP had also noted Griffiths isn't fluent in French and questioned his ability to moderate a free-flowing bilingual debate.

Mulcair said on Tuesday morning he would take part in the debate even if it was incumbent on him to ensure that his exchanges with the other leaders are bilingual.

"It now appears it's going to be on the shoulders of the participants to ensure that it's going to be in French," Mulcair said during a campaign stop in Lethbridge, Tuesday, adding, "I will ensure that it will be bilingual, that the French element will be there with the rules that they've set down."

Mulcair said he still hoped to see some moderation in both official languages.

The Liberal Party said it was confirming Trudeau's participation despite ongoing concerns over the format.

"While we continue to have concerns with the nature of the format with regards to language, there has been some accommodation," Kate Purchase, the party's director of communications, said in a news release Tuesday.

The Liberals had also raised a concern about the Munk Debates charging an entrance fee, and while the organizers did not move on that the party said it was "encouraged that the livestream will be available to anyone, including political parties, who wish to carry the debate."

Both leaders said they looked forward to debating such issues as the ongoing Syrian refugee crisis.

The leaders had until noon Tuesday to formally accept the debate invitation.

Green Party Leader Elizabeth May has not been invited to take part in the event.

May's Greens team up with Twitter

May also been excluded from this Thursday's debate on the economy hosted by The Globe and Mail newspaper.

But the Green party leader plans to muscle her way into the conversation — at least online — with the help of Twitter.

Her party will team up with the social media company to swiftly film and Tweet May's video responses to statements by the three invited leaders.

"This is one way of saying to Canadians, we're not going to give up on helping to communicate issues in a way that will engage voters," May said in an interview.

"It's the best we can do," she added, "but it's far from being a fair debate."