Hi Cliff,
Hope you enjoy the city.
Close to the airport (Pearson) you will find Aquatic Kingdom, great guys, but I find not the best selection of livestock in the city, but probably the largest store in the city by square footage (have freshwater/ponds also).
Then there's ReefRaft that is less than a block west of Aquatic Kingdom. Jay and Jenson, in my experience are great guys to deal with, has some of the nicest corals in the city, and frequently has some amazing fish.
Further west to Oakville is Oakville Reef Gallery, been there twice, not overly impressed with the service and pricing. Have no idea as to what they get in shipment wise. I personally go out of my way to avoid this place, others swear by it.
North to Markham is Sea U Marine, I would rank with ReefRaft, great selection of corals and fish selection is excellent (almost bought a Candy Basslet today). Great prices and ships Canada wide. I go there every week, and it's a 100km trek

My favourite store by far.
South east is North American Fish Breeders, John gets a great selection of corals and fish, best prices in town, get there early if there is something that is desirable, as there are lineups on shipment days. PIA to get to from the West end (traffic).
The Big Al's, I personally don't go there, there are some smaller establishments around, but I'm not familiar with them.
Happy shopping, even if it is only window
