I tried to compare the population of each city living in neighbourhoods above certain walkscore thresholds, that way you could see how easily you could live car free/car lite in Toronto's core without having to worry about Etobicoke and Scarborough bringing down the city's overall score. It looks like the neighbourhood populations they list aren't accurate though, at least for Toronto, since if you add their populations for all Toronto's neighbourhoods you get a total of 3.443 million people within the city proper. Neighbourhood populations for US cities seem pretty accurate. Nonetheless, Toronto comes out ahead of many major US cities like Philadelphia by this measure.
Childhood home: 73 (in Brampton, near Conestoga Mall and Loafer's Lake Rec Centre/Library).
Parents' home: 22 (in Oakville, I removed a bunch of bogus ammenities but for some reason the walk score didn't change)
UW Residence 1st Year: 71 (UW Place)
UW Residence 2nd year: 28 (Columbia Lake Village, it was noticeably worse)
Previous home North of Uptown Waterloo: 88
Current home West of Uptown Waterloo: 72
Future home in Uptown Waterloo: 97