Of the four contests, the byelection in Manitoba's Brandon-Souris has become a priority for the party leaders as the normally Conservative stronghold could change hands, The nomination process of Tory candidate Larry Maguire, a prominent provincial MLA, has rankled some Tories and he's facing a strong challenger in his Liberal opponent Rolf Dinsdale.
Liberal Leader Justin Trudeau has personally visited the riding three times, NDP Leader Tom Mulcair has visited twice and several federal Conservative cabinet ministers have made the trek to the riding.
Prime Minister Stephen Harper, who has for weeks fended off opposition attacks about the Senate spending scandal, took the unprecedented step of sending a personal letter to Brandon constituents — an indicator of what's at stake in this riding.
Meanwhile, the race for former interim Liberal leader Bob Rae’s riding of Toronto Centre will likely be decided by two journalists — Liberal candidate Chrystia Freeland, a former Reuters executive and author; and NDP candidate Linda McQuaig, author and former Toronto Star columnist.
In Montreal's Bourassa riding, another Liberal stronghold, the race is on to replace former Liberal MP Denis Coderre, who stepped down to run for municipal office and is the city's newly elected mayor.
The race is also seen as duel between the Liberals and the NDP with six-year Quebec National Assembly MLA Emmanuel Dubourg running for the Liberals and Stéphane Moraille, a former singer in the musical group Bran Van 3000, the candidate for the NDP.
Mulcair has personally campaigned in the riding six times; Trudeau has been there three times.
But in Manitoba's Provencher riding, candidate Ted Falk is widely expected to keep the riding Conservative territory. The longtime Tory stronghold was most recently represented by former cabinet minister Vic Toews, who retired from politics in July after almost 13 years as the area's MP.
Since Trudeau was chosen as the federal Liberal leader last spring, the party has risen from third place in the polls, back into first place, slightly behind the Conservatives. The NDP has sunk back to its traditional third-place slot.
The NDP has poured its resources into the Toronto and Montreal ridings and are hoping to make a significant dent in the Liberals' margin of victory.