If you have close access to a large American city, (and granted, from Halifax your choices are limited) I would recommend driving across the border and flying from a US city. We've done both and to my mind the advantages of driving to Detroit outweighed the disadvantages:
Advantages:
- cheaper fares, typically
- greater selection of flights
- clear customs at the border, not at the airport (this is a big one for me)
Disadvantages:
- longer drive to the airport, perhaps in inclement weather
- Mike