Air Canada has a seat sale ending tomorrow evening (October 25) while Westjet's sale ends Thursday evening.
Book before it's too late!
Westjet's blackout dates apply to flights within the Canada and the US but not to Europe, Mexico or the Caribbean. The blackout dates are: December 20-24, 26-31, 2017 and January 1-7, 2018.
Air Canada's seat sale doesn't seem to have blackout dates, but tickets during typical blacked out periods are high.
You can fly out of YYZ to NYC on Westjet for as little as $183 out and $82 back, while with Air Canada, you're looking at $151 out and $103 back.
You may want to split up your flight, one way with AC out and Westjet back, depending of course on whether you have luggage to check in and have status with one, the other or both, and of course, availability at cheap rates when you're flying out.