Couple questions...
Has anyone flown AirCanada from Halifax to Montreal and then to Orlando? The flight we are looking at has a 1.5 hour layover. Is that enough time to get through security and customs and get to our connecting flight?
Has anyone driven from Halifax to WDW? How many days did it take? Any tips?
Myself, I'd drive. It's definitely going to be cheaper if you have 3 kids. Use hotelcoupons.com to book your hotel rooms. We used that site and never paid more than $65 a night and they were clean, easy access off the highway, had nice pools and came with free, full hot breakfasts

We drove from New Brunswick, it was about 28 hours driving, which we split over 3 days, and our total cost was only $850 US, vs. the cost of parking at airport, flights, rental car etc... which were going to run us almost twice as much. We pushed it the first couple of days, and drove to PA the first day (12 hours driving), SC (around 10.5 hours driving) the next day and then had an easy, 5.5 hour drive into Florida the next day. You could definitely do it in 3 days, if you do 11-12 hours of driving each day. One piece of advice: you will be tired after driving so far, so plan on your first full day in Florida to be a "rest" day.
Another way we saved money: we have an SUV with a plug in the trunk, so we borrow an electric cooler, and stocked up at Costco with snacks, bottled water etc... for the trip down. We had free breakfasts with our hotel, and then just packed fruit, juice boxes, bread, PB, jam etc... and made all our own lunches. We just stopped at the rest stops along the highway (they have some really nice ones down south) and ate there. Was much cheaper. Also, we took a soccer ball and football with us, and whenever we stopped for lunch, bathroom etc... we'd get out and run/kick/throw the ball around for a bit. Even 10 minutes really helped stretch our legs and give us a little pick me up. This way, the only food we bought on the drive down/back was supper, and we just did quick/cheap fast food, which was only about $20 a night for our family of 4.