Previously known as the Sky Dome, the Rogers centre plays host to all of the Blue Jays (baseball) and Argos (Canadian Football) games as well as a selection of conventions and concerts. It's recently had all of its multimedia screens revamped.
The roof can open and close, so adverse weather never affects sporting events, and if the weather is nice you get to sit with a wonderful view of the CN tower. Food is available inside the Centre, but it is quite steeply priced, much better to buy a hotdog from one of the many stands outside - $2.00-$3.00 than buy food of poorer quality inside. Just remember to finish all your beverages and food before you try and get into the centre as they have a very strict policy.
If you're visiting Toronto I highly recommend seeing if there is a game that you can catch, tickets are cheap up in the nose bleeds and it is definitely an experience.