I'm indifferent about canyons. I think the more they can preserve an open/airy feeling while still increasing density, the better.
Also, a more open sky means more sunlight, which is better for trees. They should keep the skies open and green up the urban areas.
I respect that that is your opinion, but at the same time I really don't understand it. Sure, it sounds great on paper; the tower-base form allows for more sunlight and better views of the sky. However, in practice it more often than not (in my experience) results in a street that feels disjoint and disconnected. Canyons, on the other hand create a street wall that feels continuous and urban. Buildings built in this form also have the advantage of taking up more of their site area, meaning they don't have to be as tall, which slightly mitigates the sunlight/shade issue.
I had a few screenshots from street view I was going to post, but I'm having a little trouble uploading them on mobile. However, just compare the built form of Southcore to that of a city like New York, or even the older sections of the financial district in Toronto. Sure, Southcore probably has more sun, but I would rather walk in New York (and, based on built form alone, in the financial district, although the retail scene there isn't exactly booming).
Ideally, I think a city needs to develop a strong mid-rise base before going through a high-rise boom. This helps to transition neighbourhoods from low to high density smoothly rather than abruptly. It also creates a nice urban backdrop to the towers that do eventually arise. Since we obviously don't have this history in (most of) Toronto, I think we need to focus on filling in any gaps we have left with 15-20 story canyon-form buildings, to form a base in the core (transitioning to a 5-15 story base in areas just outside of the core, and eventually ~5 stories on avenues all around the city).
Anyway, that's just my 2 cents. Sorry to distract from the actual topic of this thread, which is One Bloor East - one of the few buildings in the city that I feel uses the tower-base form effectively.