This. AC knows that weather allows them to do almost anything, so uses it as an excuse as they can and will in many cases get away with it.

It reminds of my a train network system where people with a yearly pass would get an end of year rebate for any delays of over 10 minutes - say 5% of their trains were delayed, they'd get some amount (maybe 5%, I can't recall .. but something related) back.

How did they deal with this? They would cancel most trains that were to be delayed by > 10 mins. Fair, logical? Maybe not, but they could get away with it.

The answer, as has been hinted at is to challenge it. For most people that requires the knowledge and ability to either go find out (EF?) or if it were me ... I'd post here using the flight number and date (of course ) to find out the actual reason. There are exceptions of course, if I'm sitting in Toronto and have 2' of snow out the window I will expect weather delays.

If it's a dry day in July and I'm flying to YYZ-YVR; well then I'd probably post.

AC plays the odds because there is no business benefit to not doing so.