The Toronto image cuts off large areas of sprawl to the north (should go up to Barrie at least)....while the image for Chicago cuts off nothing of interest.... that kind of makes my point, doesn't it? Having said that, Toronto is more dense than Chicago, but that doesn't mean its environs aren't sprawly. Ontario felt it had to limit sprawl because it was a big problem so they introduced new legislation limiting where growth may occur in "Places to Grow". You can believe that this legislation was unnecessary if you want, while people in the know see otherwise.
More about Toronto's sprawl to the north: "Barrie has been designated an Urban Growth Centre by the Province of Ontario (Places to Grow Simcoe Area, 2009).
Its population growth, largely due to its emergence as a bedroom community for Toronto, has given rise to the development of numerous subdivisions on the southern side of the city." Barrie is 90 km north of Toronto... yet it is a bedroom community for Toronto.... that's a lot of sprawl.
https://en.wikipedia.org/wiki/Barrie