Forty days — and every one of them will count.

It's rare for a Canadian federal election campaign to begin with the outcome so much in doubt. To call the 43rd federal election close would be an understatement. On Day One, it's literally as close as it can get.

That's how things look on the surface, at least. But a deeper look suggests that the Liberals hold some advantages over the Conservatives in how their vote breaks down across the country — slim, potentially vulnerable advantages, but advantages nonetheless.

The CBC's Canada Poll Tracker, an aggregation of all publicly available polling data, has the Liberals and Conservatives tied down to a tenth of a percentage point, with 33.8 per cent apiece.

That's a reversal of fortunes for Justin Trudeau's Liberals, who at the beginning of the summer were trailing the Conservatives by five or six points nationwide. Only now, with the election finally being called, has the party erased that deficit — though it has yet to regain all of the support it has lost since the eruption of the SNC-Lavalin affair in February.

Trailing in third are the New Democrats, at only 12.9 per cent support. They are being chased by Elizabeth May and the Greens, who are running at 10.7 per cent.

Beginning at 9 a.m. ET, The National's Rosemary Barton will host special coverage live from Rideau Hall. It will be on CBC News Network and CBC TV, and streamed on cbcnews.ca, the CBC News app for iOS and Android, and on CBC Gem. On CBC Radio One, Susan Bonner and Chris Hall will have live coverage of the election campaign kickoff starting at 10 a.m. ET.

The Greens have been maintaining the support they picked up earlier in the year after a series of breakthroughs in provincial elections and in a federal byelection in British Columbia in the spring.

Their trend line has been largely flat over the summer, however, while that of Jagmeet Singh's NDP has ticked slightly downwards — increasing the perception of a two-horse race between the Conservatives and Liberals and partly explaining the heated exchanges between the New Democrats and Greens in recent weeks.

The Bloc Québécois and People's Party stand at 4.4 and 3.3 per cent, respectively.

National tie likely means Liberal edge in seats

The dead heat between the Liberals and Conservatives masks some of the lopsided regional battlegrounds across the country.

Andrew Scheer's Conservatives, for example, hold a lead of 40 points in Alberta and nearly 24 points in Saskatchewan and Manitoba. Altogether, the Poll Tracker estimates that would deliver around 55 seats to the Conservatives.

The Liberals' lead of six points in Ontario and 14 points in Quebec likely would deliver around 121 seats at this point — enough on its own to put the party most of the way toward a majority government.

Still, current polling suggests neither party is in line to win the 170 seats needed for that majority. The numbers suggest roughly 164 seats going to the Liberals and 140 going to the Conservatives.

That's a close margin and it wouldn't take much to flip a dozen or so seats — turning a Liberal minority into a Liberal majority on the one hand, or a Conservative plurality on the other. For that reason, the Poll Tracker gives the Liberals only a 65 per cent chance of winning the most seats if the election were held today, and gives the Conservatives a 35 per cent chance.

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Much will depend on the performance of the other parties. The New Democrats are neck-and-neck in the projected seat count with the Bloc — the NDP is projected to win around 14 seats and the Bloc about 15. That means both parties will have in mind the threshold of 12 seats needed to be a recognized party in the House of Commons; the Bloc is hoping to pass that threshold and the NDP is hoping not to fall below it.

The Green Party is the wild card. The party is currently favoured in four seats and is considered competitive in as many as eight. The Greens are the only party that can claim to be in a significantly better position than four years ago. Their success or failure in making good on those numbers will have big implications for the New Democrats and Liberals, the two parties that have been hurt most by the rising Green tide.

Liberals lead in Ontario, Quebec, Atlantic

Ontario is a big part of the Liberals' seat advantage, with the party holding 39 per cent support in the Poll Tracker to 33 per cent for the Conservatives. The NDP trails with 14 per cent in the province, followed by the Greens at 10 per cent.

While that represents a six-point drop for the Liberals since 2015, the Conservatives are also down in Ontario. The party captured 35 per cent of the vote in the province in its losing campaign four years ago.

In Quebec, the Liberals are holding their support from the last election with 36 per cent. The Conservatives follow with 21 per cent, the Bloc Québécois with 19 per cent and the Greens and New Democrats with 10 per cent each. That's more than a 15-point drop for the NDP in Quebec — putting every seat the party holds in the province at risk.

The Liberals are on track to lose seats in Atlantic Canada, where they are at 41 per cent support — down 18 points from the last election, when the Liberals swept all 32 of the region's seats. The Conservatives have nearly doubled their support in the region to 31 per cent, while the NDP is struggling with 10 per cent of the vote. That puts them in fourth behind the Greens, who are averaging 14 per cent support in the polls in Atlantic Canada.

Conservatives ahead in Alberta, Prairies

The Conservatives are in a better position in their western strongholds, with 59 per cent support in Alberta and 47 per cent in the Prairies overall. The Liberals trail with 19 and 24 per cent, respectively. The New Democrats are scoring only 10 per cent in Alberta and 16 per cent in the Prairies.

British Columbia is shaping up to be the most hotly-contested province. The Conservatives hold a narrow lead with 32 per cent, followed by the Liberals at 30 per cent. The two parties are fighting over a number of seats in the Lower Mainland and the B.C. Interior.

The NDP is in a narrow lead for third place with 17 per cent, followed by the Greens at 16 per cent. The Greens are threatening the NDP's stranglehold on Vancouver Island, while the party's drooping numbers in B.C. could put seats in Vancouver itself at risk of flipping to either the Liberals or the Conservatives.

An election that could come down to the margins

This is where the campaign stands today. There is plenty of scope for things to look radically different in another 40 days. The electoral landscapes at the dropping of the writs in 2011 and 2015 bore little resemblance to how they looked on election night.

Voting intentions shifted dramatically in each of the last two campaigns. That doesn't necessarily mean they will this time. Either way, the next 40 days will tell the tale.

A few specific parts of the country can be expected to have an outsized influence on the results. With about 30 seats, the suburbs around Toronto likely will decide who gets to form the government. The Liberals won most of these Greater Toronto Area seats in 2015. In 2011, it was Stephen Harper's Conservatives who nearly swept the region.

In Quebec, the francophone seats between Montreal and Quebec City could determine whether the Liberals or Conservatives can secure a majority government. The collapse of the NDP's support has turned the region into a three-way race (including the Bloc).

These are just two of many battlegrounds in this election. Until the logjam breaks (if it does) the Liberals and Conservatives will be fighting at the margins, hoping to gain the slightest of advantages in regions of the country that swung most sharply between the 2011 and 2015 elections.

After four years, it all comes down to the next 40 days.