Because Toronto is the largest market in Canada.
I accept Toronto is the largest market, but under phase 3 and 4 plans there is no fan involvement, no interaction with the public and media is done by videolink and zoom.
How would anyone notice a difference if it were in Toronto vs. Vancouver vs. Edmonton?
They could be playing 4 games per day anyway, so the time zone isn't that big a deal under artificial circumstances.
The biggest difference might be that when the hotel staff start coming down with Covid no one would care much in Toronto, whereas that could be a bigger deal in places where it's under better control.
If groups of players start going into quarantine during the tournament it's going to be a gong show anyway.