Head down towards Niagara - but avoid the Falls! Well, you can stop to look at them, but they are incredibly kitchy. Niagara-on-the-Lake is touristy as well, but in a much better way, since it revolves around the wine region, and there are plenty of music/acting festivals and events throughout the entire summer. Every vinyard (there are 40 or 50 VQA ones in the area) gives free or cheap (1$) tastings of their wines, and you can get some amazing stuff for not too much. The town has some great little shops, too, although things are somewhat expensive. The Shaw festival runs throughout the summer, and it might be interesting for your family to catch a show there.
Also, there’s the Stratford area and their festival - primarily Shakespeare, but also a lot of local playwrites put on performances.
For the kids, you might want to consider a day trip to Canada’s Wonderland - especially if you’ve been doing a lot of “adult” things. It’s your generic theme park, but it can be a lot of fun.
I totally agree that Guelph is a great city to visit (though I won’t be on campus at that time of year to see you! hehe). It has several festivals as well, and some great little shops. The vegetarian restaurant overabundance isn’t all THAT bad, though I do find it a little bit funny considering the presence of the Ontario Agricultural College and Veterinary Colleges in town. I think you can get tours of the OVC if you call ahead - but I’m not 100% sure about how it works. The Sleeman brewery is a lot of fun, too.
Hamilton has a great Royal Botanical Garden. It’s not that expensive - I think it’s 8 or 9$ for adults, less for kids -and it is really beautiful. I went only once last summer, but I plan on going back again a couple of times this summer to see the various gardens in their prime. This webpage (http://www.rbg.ca/pages/visit_bloom.html) has information on what is best to see at each time of year, and when you go, they will tell you at the gate as well. I saw the Rose Garden and Rock garden, though the roses were at the end of their season. There are a LOT of kids activities there.
In Toronto itself, there are always things to do, though the Ontario Science Centre is a much, IMHO. www.ontariosciencecentre.ca . I spent a whole day there last fall, and I didn’t get to see everything! The prices are really reasonable - adults 18$, teens 12, and kids 10. Its almost more expensive to go see a movie around here!
There are a bunch of other things, but that’s a start for you!
Have fun!