We always flight out of Dorval. We've never been very lucky with deals but we always find a flight in Business from Delta cheaper or equal to the direct flight from Air Canada Rouge in the past. The schedules are not too bad either, you can get in early on the first day and leave late on the last to maximize the time in the parks. The only thing is the exchange rate is not in our favour this year so this might not hold. You can always check to fly out of Burlington, it's a really nice and quaint airport.