The downside of Bike Share Toronto is that it requires a credit card. That isn't big deal for locals, just be aware that there may be foreign currency transaction fees for those of you who aren't from Canada.You also have to be comfortable riding a bike in a big city where you'll be dodging cabs, pedestrians, bikes, etc. The Bike Share Toronto website has all sorts of details on how to use the system and here are some maps indicating the stations nearest the TIFF Venues.
Before you rent a bike you should check the website to make sure the dock at your location isn't full. iPhone and Android apps for bike availability are also available.
Isabel Bader Theater: 93 Charles Street West
Jackman Hall, Art Gallery of Ontario: 317 Dundas Street West
Scotiabank Theater: 259 Richmond Street West (Use "The Ballroom" for theater location reference on map below)