NDP Leader Thomas Mulcair will have to make big inroads in Ontario if he wants to defeat Stephen Harper and become prime minister. (CP)

So Thomas Mulcair is the new leader of the NDP. Now what?

With the party's gains in Quebec now secure, at least for the time being, the NDP under Mulcair can turn its attention to making the inroads in the rest of the country.

Quebec was always going to be key to any hopes for an NDP victory in 2015. With 58 seats in the province, the New Democrats only need to win a little more than 42 per cent of ridings in the rest of the country in order to form a majority government.

PHOTOS: BEST SHOTS FROM THE CONVENTION

Polls have suggested only Thomas Mulcair was in a position to consolidate the NDP's position in Quebec. New surveys from the province will have to confirm that, but that fact that Mulcair gave his first media interview to Radio-Canada and recited the first part of his victory speech in French, makes it clear he is not taking his party's Quebec support for granted.

The New Democrats are already in good positions in a few regions of the country. The party has been leading in about half of the polls released in 2012 in Atlantic Canada, and could pick up a few extra seats in Nova Scotia, New Brunswick and even Prince Edward Island. Thomas Mulcair received the support of former or current party leaders from every province in the region before Saturday's vote, and polls suggest he was one of the favourite candidates among Canadians living on the east coast.

The NDP has also led in British Columbia in about half of the polls released so far this year, and the province is setting up to be a major battleground in 2015. The provincial New Democrats under Adrian Dix look set to form the government next spring, and if voters are impressed with Premier Dix they might be more likely to vote for a prime minister Mulcair.

In the Prairies, the New Democrats have been polling above their 2011 election result. The hegemony the Conservatives have maintained in Saskatchewan looks to be in serious danger, particularly if the riding boundaries are re-drawn to give the province some true urban ridings.

However, these three regions, plus Quebec, are not enough to put Thomas Mulcair at the head of the first federal NDP government. The real challenge for the new NDP leader will be to conquer Ontario.

The province has yet to warm to the federal New Democrats. Even in his last stellar campaign, Jack Layton only managed to narrowly edge out the Liberals for second place in Ontario, and the party was still almost 20 points behind the Conservatives. Since then, the Liberals have moved back into second place. Thomas Mulcair will need a major breakthrough in the province in order to win the 50 or so seats he will need there in 2015.

That might be too much to expect from a rookie leader. A more realistic goal may be to win enough seats to defeat the Tories with the help of the Liberals. But Thomas Mulcair was always going to have big shoes to fill. With a personality that has earned him the nickname "Grizzly," Canadians can be certain he'll try.

Éric Grenier taps The Pulse of federal and regional politics for Huffington Post Canada readers on most Tuesdays and Fridays. Grenier is the author of ThreeHundredEight.com, covering Canadian politics, polls, and electoral projections.

PHOTOS: THOMAS MULCAIR

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• Thomas Mulcair

  NDP Leader Thomas Mulcair comments on the federal budget in the Foyer of the House of Commons on Parliament Hill in Ottawa Thursday March 29, 2012. If there was any doubt that Thomas Mulcair's political universe revolves around Quebec, it was dispelled by his response to Thursday's federal budget. (THE CANADIAN PRESS/Adrian Wyld)

• Thomas Mulcair

  NDP Leader Thomas Mulcair addresses the Economic Club of Canada in Ottawa, Thursday April 5, 2012. (THE CANADIAN PRESS/Fred Chartrand)

PHOTOS: BEST SHOTS FROM THE CONVENTION

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