In their 737, it's 29" with pretty narrow seats, and it's horrible! Took them for a flight to Cuba in April, it was not too bad for me (5'4"), but my 5'11" 220lbs friends felt pretty cramped. Try to reserve the Extra Pitch if it's available and you can fork the extra money, especially if anyone in your family is tall or broad shouldered.
See there, and check which plane you'll take (but standard pitch is only there for the 737):
http://www.sunwing.ca/SeatSelect.asp#