As a Saint Johner, I definitely don't consider Halifax Stanfield an option when I'm shopping for flights. If Fredericton or Moncton happens to offer favourable prices or timetables, I will choose to fly out of there, but the extra few hours it would take to drive to Halifax just aren't worth any additional timetable or destination benefits it may offer. This is why the suggestion is often made that southern NB would benefit from a central airport in the Sussex area to serve all 3 cities.
A lot of people I know in SJ do indeed fly out of Bangor if they're going to US destinations, as the airfare savings can be significant, but I haven't heard about anyone who's made the drive to Halifax for a flight. Sorry guys