750 Miles gives you tons of options from provincial parks to major cities. Just remember that if you decide to go anywhere east of Toronto to plan to avoid going through during rush hours. Even avoid weekdays if you can. If you are near Toronto and want to sight see in the city definitely take the commuter service in rather than driving.
GO TransitToronto also has an excellent transit system
Toronto Transit Commission but there is lots to see and do within walking distance of the train station.
Not knowing your interests here are just a few suggestions;
1. CN Tower
2. Take in a Blue Jays baseball game.
3. Hockey Hall of Fame.
4. Eaton Center, (Major indoor shopping mall)
5. Roundhouse Park (Toronto Railway Museum & Steam Whistle Brewery)
6. There are several live theater venues.