Had a MARVELOUS time! Seriously I cannot recommend this ENOUGH. The entire trip I could not turn off the inner-writer and kept composiing a travelogue in my head. Short version: stay in the Clifton Hills area - it's a must. It is also about half price in early June as at any other time in the summer. We were minutes from the Falls, museums, and all by foot and paid less than $100 per night for a two-room suite. Travel with family you really love so that sharing a two-room suite isn't a problem. :)
Walk everywhere except to dinner. It's worth the savings - even at $4+ per gallon (litre, whatever) and drive just ten minutes out to pay far less for dinner. Tim Horton's is the only breakfast you will ever need. Get the Fruit Explosion muffin or cruller (or heck, both). You won't be sorry. Your waistline is another story, however.
Feed the one-footed seagull. We know him as "stumpy."
Read the plaques. We called it the "Death and Nature's Destruction" tour but we learned a ton. Our daughter was up at 6:00 a.m. our first day home, just itching to Google for more information on the stories we had read.
Buy the passes. I'm usually uber-resistant to being told what to do but the Adventure Pass packages include a day's free transportation and admission to eight attractions for a fraction of the per-site price.
The Butterfly Conservatory is way cooler than you'd think. If, however, you are a teenager with a low tolerance for winged things flying at you, it may not be for you.
Pay attention to the heritage sights. It's eye-opening to realize that Americans were the "advancing forces" they were keeping at bay in 1812. Sure, the Canadians have pretty much forgiven us by now, but it was an interesting spin on our normally American-centric view of history for both young and old(er) alike.