Since you live in Hamilton, I would consider flying out of either Buffalo OR Detroit. Yes, it would take you 3-4 hours to drive to Detroit, depending on traffic, but it gives you another U.S. airport to check for low fare deals.
If you want to fly, research EVERY airline that flies out of both airports to Orlando - the most likely discount carriers include Southwest, AirTran, JetBlue and Spirit (there are probably others that I'm not thinking of at the moment).
Go to each of their websites and sign up for ANY of their promotional mailing lists. I have heard of people getting Southwest fares from Buffalo to Orlando at $49 each way, and this is not entirely unheard of - depending on the time of year that you are travelling. When we went in '06, I acted too quickly, booking our flight 3 months in advance at $79 each way (from Detroit) on non-refundable tickets. 6 weeks before our vacation, I saw an online offer for $39 each way!!!! Yeah, I was kicking myself.
To decide whether to fly or drive, I suggest the following.
Estimate the cost of gas, food and (if not driving straight through) lodging. Depending on your fuel economy, the type of motel you use and the number of people (in terms of food costs), I've seen most estimates range between $300-$600 USD for a family of four.
Second, estimate the cost of flying (get a range of the maximum you would pay by getting virtually no deal on the flight vs. one of the best) and then add the cost of gas to the airport and the cost to park your car there. For us, using Detroit, as a family of four our total cost will be between $625 and $950.
Usually, for a family of four, flying will probably cost $200 to $300 more than driving, but could be close to break even if you stay at a nice motel, eat a lot, and get lousy milage with your vehicle.
Finally, even if it costs more, is it worth the cost to effectively cut your travel time in half (if you do not drive straight through)? I know that I feel lousy the day after driving a lot, so even my first full day at Disney wouldn't be great for me - but that's me. Others don't mind driving.
Anyway, there is a lot to consider, and way too many factors to say what is best for your family.
Good luck on the decision, and I hope you have a great time!