While it doesn't advertise itself as one, to me House On Parliament is the closest thing to a gastropub in Toronto.
Unlike others that actually advertise themselves as such, they don't try to create fancy menus and compete with the latest fusion restaurant. It's just a nice little pub, cozy on the inside, a comfortable outside, with a menu of simple, standard pub food (see steaks, burgers, curry, pork chops etc.) prepared extremely well.
I always go for one of the daily specials and have never been let down.