TORONTO -- It's enough to give any city a big head, let alone one that already -- only partly self-deprecatingly -- dubs itself the "Centre of the Universe."

All three parties have been working feverishly this election to win the affections of the Greater Toronto Area, which holds a high concentration of seats in play and where each party sees potential paths to victory.

The appeal of Greater Toronto Area votes largely boils down to a numbers game: there are 25 seats in the city alone -- about double that when the surrounding communities are included.

In reality, the mythical GTA is home to a few, distinct fights.

First, there is the "416," that includes core downtown and old city of Toronto ridings where the fight is NDP versus Liberal.

Travel a bit further away from the centre of the city to the Etobicoke, North York and Scarborough suburbs and the Liberals contend with the Conservatives.

Then there is the "905," the massive, ethnically diverse suburbs that include Brampton and Mississauga. This area too has shaped up to be a Conservative-Liberal race, where the Grits are eager to win back a large swath of longtime Liberal seats that turned Tory blue in 2011.

Finally, there are areas a little further away from Toronto -- in Hamilton, Kitchener-Waterloo, Oshawa and beyond. There is a mixed bag, with the NDP seeing more opportunity in some of those constituencies than in the suburbs that can see the CN Tower on a clear day.

Liberal and Conservative insiders who spoke candidly to The Canadian Press say the 905 in particular has become a "dogfight," with ridings that appeared to be solidly Conservative in 2011 suddenly appearing to be more tenuous.

John Mykytyshyn, a longtime Tory organizer and activist, said the GTA story on election night will come down to hyper-local dynamics including who has kept their voters list up-to-date.

"The local candidates have an opportunity to make a bigger difference than ever, and I think you're going to see the difference on election night where there's surprise wins or surprise failures," said Mykytyshyn.

"When you do the analysis two weeks after the election ... you'll find out who were the hardest working MPs, who were the ones that took it for granted, who were the stellar candidates who knocked on every single door versus the incumbent who thought they had it in the bag."

There are at least half a dozen ridings in the GTA that were won -- mostly by the Conservatives -- by fewer than 1,000 votes in 2011. With many other ridings redistributed and several other new ones created in the GTA for this election, it makes for a dynamic battleground.

The NDP needs to hold onto the Toronto seats it already has and is hoping to gain several more, including the new Spadina-Fort York -- the heart of Toronto's booming condo-land -- where Olivia Chow is up against Liberal Adam Vaughan.

"There are a couple of key races where the NDP are hoping to pick up seats," said NDP pundit Marit Stiles.

"So yes, the NDP only needs 35 seats on top of what we (won in 2011) ... so if you look at it that way then absolutely, any seat we can gain, any ridings we can gain in the 416 are extremely important."

To that end, the New Democrats released a Toronto-specific platform, highlighting the promises that they believe will be beneficial to area voters.

Liberal candidate Navdeep Bains, who has also done organizing for the party in the 905 area, argues the Liberals have succeeded in harnessing the vote for change. The party lost several ridings in the region due to vote splitting, although some were clear, majority wins for the Conservatives.

Part of the Liberal appeal, says Bains, has to do with their platform promises on immigration.

"The fact that (the Conservatives) have let down many, many people with creating so many obstacles for immigrants, particularly in the area of family reunifcation, we came forward with meaningful changes in policies around that that have been well received," Bains said.

Liberal infrastructure and transit promises, as well as its Canada Child Benefit, are also being showcased to GTA voters.

But one issue that may throw a wrench into Liberal plans is not even federal.

Groups of parents, mostly in the 905 and suburban Toronto regions, have been protesting a new provincial sex education curriculum that was updated to include the perils of online bullying and sexting as well as introducing the concept of same-sex relationships in Grade 3.

Lessons on gender identity and, later on in the curriculum, mentions of anal sex have been particular lightning rods for controversy.

But whether the parents who flooded the lawn of the Ontario legislature to demonstrate this spring or pulled their kids from class in protest are a vocal minority or form a powerful voting block in some ridings remains to be seen.

Jotvinder Sodhi, one of a dozen parents protesting outside a massive rally Liberal Leader Justin Trudeau held in Brampton earlier this month, used to vote Liberal both provincially and federally but no more, he said.

"If it's a provincial issue, (federal politicians) still have a voice to raise, as well as concerns to raise with the other level of the government to resolve it," he said.

Earlier this year, Wynne said she believed the federal Conservatives were using sex ed as a political wedge issue in the province in advance of the election.

Indeed in Brampton, Conservative MP Kyle Seeback sent out a mailer to his constituents questioning "the age appropriateness" of the curriculum.

But the broad voter concerns candidates are hearing as they canvas tend to be more about jobs, the economy and transit infrastructure.

Albert Thomas, a Brampton resident and immigrant from Jamaica, said when he arrived in Canada he was "taken aback" by the inadequacy of public transit.

"I went to school in the UK, so I thought it was the same in terms of infrastructure and the same transportation system. Come on," he said dismissively.