It seems to me there were a few reef stores when I was in Toronto for a couple days last year. I just looked them up on yellowpages.ca.
But, two that come to mind off the top of my head are ReefRaft and Oakville Reef Gallery ...
reefraft.ca
oakvillereefgallery.com
I randomly drove by some place that was in Richmond but I can't remember the name of it.
Sorry ...
Also I think fragalot.ca and wickedfrags.ca are in Toronto, don't know if they're thrilled about drop-in visitors but might be worth contacting and asking if you could pop by. I know I would.
Enjoy your trip and if you find any other stores in the area let us know! Although I don't if I'll be going back to Toronto anytime soon, it never hurts to know where to go visit in case one ever does go...