If you are a sport fan, Toronto has something for you, no matter what major league sport you follow. The Air Canada Centre hosts the Toronto Maple Leafs, one of the original 6 teams of the NHL. They also host the Toronto Raptors, the Basketball team. The Rogers Centre (formerly the Skydome at the foot of the CN Tower) hosts the Toronto Blue Jays (baseball) and the Toronto Argos (Canadian Football League). The new BMO field hosts the Toronto Football Club (aka soccer). There's also a league lacross team in town. Every summer, Toronto hosts the Rogers Cup tennis tournament. Tickets aren't cheap and are not always easy to get but if you're vigilant you will succeed!
For Hockey fans, there's the Hockey Hall of Fame museum on the waterfront. Every year there's also a Sportsmen's show for fishing and outdoor sports. Of course in addition to the professional sports teams, there are lots of local and minor league teams to follow and lots of places to participate in various activities including tennis, swimming, volleyball, gyms, etc.