I'm just back from a business trip to Toronto, which is a nice and reasonably walkable city (although I was unpleasantly surprised at the homeless problem there. Somehow I expected Canadian cities would have a better handle on that.) However, I found a significant difference between a reasonably pleasant pedestrian experience in Toronto and an outstanding one in Montreal. Why? In large part, gaps in the streetscape. Toronto has some nice destinations to walk to and ways to get there, but there were too many breaks in and between areas with aesthetically appealing walking areas.
For instance, Toronto has a lovely street, Elm Street, filled with restaurants and trees sparkling with lights in the evening. But it's only a few blocks. It feeds into Yonge Street, with a fair amount of pedestrian nightlife ... but around that, there were lots of breaks in interesting things to see on foot. In the few blocks between that area and our hotel, it was pretty dead, with business buildings interspersed everywhere (killing off the night streetscape) and parking lots or garages deadening the aesthetics. Likewise, when we took a walk down to the Hockey Hall of Fame, there was a similar problem -- too many uninteresting areas sprinkled in, making the walking experience possible but not compelling.
Contrast that with Montreal, where you can walk for a long time seeing reasonably appealing streetscapes, without major breaks for huge parking lots or blank walls of parking garages. It's a good lesson in the need to plan the overall impact of an entire district, not just building by building or even block by block, to create an outstanding pedestrian experience.
Despite this, though, I do have to say it's entirely possible to walk around Toronto -- I was especially impressed at the thought given to sidewalks in underpasses, which were much more appealing than the typically creepy walkways you find in many places around the U.S.