[hipster duck]

This is not based on anything other than a wild guess, but I expect the Greater Toronto Area (aka: the GTHA) to max out at about 12-14 million. I expect the City, based on its present-day borders to max out at about 4 milliion.

In the case of the latter, that would be a growth of about 1.2 million people, which, based on current occupancy levels, is almost the same as adding about 700,000 dwelling units. Given that Toronto adds 12,500 units a year (give or take), I think that's incredibly ambitious.

All cities hit the population glass ceiling eventually. In the 1960s, experts thought that Los Angeles would overtake NYC to become the biggest metro in the US by 1975, and have 19 million people by 1990. Neither of these prophecies has come true. But, at the time, Los Angeles had experienced astounding levels of growth for over 50 years and there was no sign that that would stop. Of course it did stop and, in hindsight, it's not hard to see why: there are limits to an outwardly-expanding automobile city until the edges are so far away that they really cease to be part of the metropolis in a meaningful way. When you have a 200 km long sprawl where citizens on one end wouldn't dream of visiting the other side without staying in a hotel, there's only so much appeal in growing further out, and it starts to get hard to qualify all of those people as "belonging" to one city region.

In Toronto's case, I think that the region is limited by very path-dependent thinking on infrastructure and growth along set corridors as well as the inability to upzone. When it comes to infrastructure and where to put growth, the thinking is that the city can jam ever more people onto a handful of overstressed transportation corridors - most notably the 401 for goods/car traffic in an east-west direction and Yonge street for transit/high density growth in a north-south direction. While the region has other corridors, added maybe too little, too late, private growth and movement remains stubbornly committed to those two. This is different from, say, London, Paris, New York, Tokyo or Shanghai, where there was never a set road that growth and vibrancy was supposed to happen on, so a spaghetti web of roads and rail lines allowed for a blob of dense growth to spread out like a carpet rather than a thread.