My wife and I and our two kids just came back from WDW, and we drove. It's much easier if you take your time, but it is 4 extra days each way. We actually drove home in 3 days back, and it was too much driving straight through.
We've done the YHZ -> Montreal -> Orlando as well, but I will never fly Air Canada "Rouge" again. I'm 5'10", and I was touching the seat in front of me with my knees. I couldn't imagine being taller.
We're about to Head back in January, and found the Wesjet direct flights look great, but they arrive way too late on the YHZ -> Orlando leg. I want to arrive in the morning.
I found a direct flight on Saturday mornings with Air Canada that is much much better, as we arrive around 10am. It gives us almost a full extra day. I am wondering if that is a normal schedule for these airlines, because I plan to take that flight every time if it's available.