What does it say in the owner's manual? Usually they spell out the exact criteria for the "special" schedule - trailer towing, operation in dusty conditions, driving in mountanouis terrain, driving in extreme cold, short trips, etc.
If none of those apply to you, then the regular schedule is what Ford recommends. While I'm sure the dealer would love to see you every three months, all you need to do to keep your warranty in good standing is to follow what Ford says in the manual.
If you want my two cents, though, I always follow the special schedule for my cars. Better safe than sorry, IMO, and it's true that the Canadian environment is pretty harsh on vehicles.