If you do the Toronto trip, hit the aquarium...it's located very close to the base of the CN Tower/Skydome, it's pretty amazing. Also nearby is the historic Brewery District for doing some 'sampling' and having lunch. I'd suggest Mill St. Brewery as a starting point...
Casa Loma, Royal Ontario Museum(ROM), Science Centre, Centre Island are a few places in Toronto you might like.
In Niagara, besides the actual falls, the Butterfly Conservatory is quite interesting as is Niagara-on-the-Lake. As mentioned, this is where you'll find many vineyards and the town itself is very quaint...touristy but not in the cheezy way.
