This one didn't live for more than an hour, so probably few bookings were made. They should definitely honor it, did you see the regular prices YYZ-Europe, they are in the $500s with AA and others, so, this was an ok discount for Europe. They will fill up some seats, especially in the low Nov-March season.

FYI, there is no need to play around with the AC site and other not user friendly sites, use Kayak and Expedia. For weekend bookings from Friday on Expedia offers free online cancellation until midnight Monday, no need to talk to humans, and you have four days to decide.