The Toronto International Film Festival will be happening the same weekend as the wedding! If you happen to find the time around all the wedding goings-on, it might be worth seeing if you can get tickets when they go on sale on August 26th. Though look out, they go fast!
A very good museum. They have an exceptional early life (pre-dinosaurs) section, which contains probably the best Cambrian display you'll ever see, as Canada is home to the Burgess Shale (the most extensive fossil record of Cambrian life. A very big deal!)
I had a peameal bacon sandwich at the St Lawrence Market only once before becoming vegetarian, but it was pretty good from what I recall! And even if you want to try something else, the market is worth visiting if you get the chance, it's got a lot going on.