There's certainly land within close proximity to Toronto that could be used if there were political will. Georgetown is closer than Bletchley Park and already has a (terrible) train connection. Nobleton is like 10km from Vaughan, well within easy reach.
If you look at other Canadian cities there are even easier wins. Calgary has empty land (not parks, not reservation) within 8km of downtown. Winnipeg is practically a model city for this kind of treatment. Vancouver and Montreal are the only obviously difficult ones due to their geography.
You have to build something self sustaining and that requires jobs in the new city. You can't just have a connection to an existing city. You need an industry or institution or something there to attract workers and the workers to support those workers.
People commute from Canterbury to London, which is > 50 miles. But they have over 100 trains a day, many of them high speed.
Reasonable commute has a different definition for different people. Some people don't commute for work, so two hours to city center is fine if they only go a few times a year. Some only commute for work a couple times a week and an hour and a half sucks, but is doable if the housing is better enough on whatever dimension. Some will be able to move their job to the new location.
If the new town has appropriate zoning and desires, a handful of companies in the city center may setup offices there to reduce office costs and attract workers that are in the periphery, instead of making everyone go into the city center.
This definitely happens around Toronto, just from looking at the density of roads on Google Maps. There's plenty of pockets of density in lines out from Toronto, and there's also several named places where there's no clear boundary between the names (there probably is at other levels of detail).
