Liberals look set to hold their two seats and might pick up a third in the upcoming federal by-elections, according to a new poll.

Voters in four ridings cast their ballots Nov. 25, in Montreal's Bourassa riding, Toronto Centre, and Manitoba's Brandon-Souris and Provencher.

The biggest upset may be in the Tory stronghold of Brandon-Souris, where a new Forum poll has Liberal Rolf Dinsdale leading Conservative Larry Maguire 44 per cent to 36 per cent. That lead has grown slightly over the last month, in a riding once held by Mr. Dinsdale's father, a Progressive Conservative, for 31 years. The NDP's Cory Szczepanski was the pick of 9 per cent of respondents. The results, gathered by interactive voice response (IVR) telephone polling on Thursday, are considered accurate within four points, 19 times out of 20.

Story continues below advertisement

If the Liberals do win the riding, it will be a massive jump in support from the last election. In 2011, the Liberal candidate in Brandon-Souris got 5 per cent of the vote, putting him in fourth behind the Greens.

The riding has been beset by allegations of Conservative infighting and controversy around the nomination process. NDP Leader Thomas Mulcair and Liberal Leader Justin Trudeau both visited Brandon-Souris to stump for their candidates on Wednesday.

The other potentially close race is the battle of journalists in Toronto Centre, where Liberal Chrystia Freeland, a former Reuters editor, had the support of 47 per cent of respondents, followed by 32 per cent for the NDP's Linda McQuaig of the Toronto Star. Conservative Geoff Pollock was the choice of 16 per cent of respondents.

In that riding, 832 respondents were contacted and the results are considered accurate within three points, 19 times out of 20. Rival pollster David Coletto of Abacus recently questioned the accuracy of IVR surveys conducted in Toronto Centre, one of the country's younger ridings, as the automated calls would target landlines and miss young residents who only have cellphones. In Forum's poll, older residents were more likely to vote Liberal, while those between 18 and 34 were split between the incumbents and the NDP.

Lorne Bozinoff, president of Forum Research, said in an interview that the way the firm weighted its results would correct any demographic issues.

Forum correctly called the results of three federal by-elections held last fall.

The NDP's ground game and get-out-the-vote efforts may be the deciding factor in the riding, Mr. Bozinoff said, pointing to the provincial party's breakthrough in this summer's London West by-election.

Story continues below advertisement

The Montreal riding of Bourassa, the site of intensifying campaigns between the Liberals and NDP, appears set to remain in the Liberal fold, with 50 per cent of respondents supporting Liberal and former MNA Emmanuel Dubourg and 21 per cent choosing the NDP's Stéphane Moraille, with the Bloc Québécois's Daniel Duranleau in a statistical tie with 20 per cent. The results are considered accurate within six points, 19 times out of 20.

Conservatives appeared to have a lock on former cabinet minister Vic Toews' riding of Provencher, with candidate Ted Falk consistently polling above 50 per cent. The Liberals were second in the poll with 30 per cent and the NDP followed at 10 per cent. The results are considered accurate within five points, 19 times out of 20.

The by-elections were triggered after four resignations over the summer: Liberal Denis Coderre, who ran for and won Montreal's mayoral election; former interim Liberal leader Bob Rae, who is representing First Nations in talks with the Ontario government about the Ring of Fire development; and Conservatives Merv Tweed and Mr. Toews, who both left electoral politics for the private sector.