Ya, we’re not talking about settling the Yukon or northern Manitoba in large numbers. There are loads of small-to-medium sized cities across the southern portion of the country. Imagine if even a fraction of those people needlessly crammed into the GTA had settled in, I dunno, Sarnia, ON or Saint John, NB instead. You could have had another important urban center while alleviating a ton of the traffic and housing issues that Toronto has. (None of those bedroom communities that the GTA sprawls through are there for geo-economic reasons – they grew across a barren wasteland just because they are close to Toronto).
The US has many of these absurdities too with New York and Los Angeles, but the national population isn’t nearly as concentrated there as compared to the GTA.