I remember a few years ago on this forum someone asked about driving through Toronto. They asked if the highway that went through it was a 'good road' or whether it was a 'narrow track that wound its way through the wilderness'!
That road is actually the busiest road in all of North America and Toronto itself is the fourth largest metropolitan area in USA/Canada. It's a huge, clean, cosmopolitan city with many diverse and interesting neighbourhoods. The CNN Tower is well worth a visit, make sure that you go to the UPPER observation deck and don't forget to jump on the glass floor to scare your fellow visitors! There is a great aviation museum at nearby Hamilton,
Link which you will go past just before you get to Toronto. It has a great selection of aircraft, including one of only two flying 'Avro Lancasters' in the world. Think B17, but much much better! There is also a WWII destroyer that you can tour down on the waterfront
Link. Back in Toronto, if you like castles
Casa Loma is worth a visit.