Originally Posted by
YOWgary
"The best day to book" is the day the seats are released, before anyone else has had a chance to get 'em. Unfortunately, this isn't on a set schedule. It's supposed to be 330 days before departure, but in practice it's been more random than that. So, start checking at 330 days out, but don't give up if you don't see them at that point.
330 might be the number with many airlines, but for flights on AC metal, it's normally 355 days out when they start releasing seats for Aeroplan redemption.