[Innsertnamehere]

The reason the GTA dominates so much is that it acts as the country's "gateway" in that most immigrants move to the GTA before going to other parts of the country.

If you look at internal migration statistics, Toronto actually exports more people to the rest of the country than it imports. It's growth is entirely (and then some) driven by immigration. Falling natural growth levels impacts the rest of the province / country, as they are more reliant on it for population growth than the GTA.

You can see this with the Liberals increased immigration rates over the last few years as well. Toronto's growth rate has increased almost in step with the increases in immigration.

People move to Canada, start in Toronto to get their footing with education, work experience, etc., then hit the road and move out to either another province or into southwestern Ontario / Ottawa, fleeing high cost of living. A lot do stay too, especially if they can find success and build a quality life in the city.

Toronto is building about 50,000 housing units a year. I think it's actually supposed to pass 70,000 this year, at least it was pre-covid. As long as that continues, people should be able to continue to move to the city.

As long as immigration continues, Toronto's growth should too. Will it hit 15 million in 2051? who knows. But 30 years ago, The golden horseshoe had a population of about 6.5 million, compared to about 10 million today. Even just extrapolating that gets it to 14 million in 2051..