The CTA has recently made and published some APPR decisions that found WestJet responsible for situations "out of their control", including
weather,
unavailable crew due to illness, or
assorted delays (including unsubstantiated crew availability).
While the CTA is rivaling Air Canada for mediocre On Time Performance, if one isn't satisfied with the airline's response, the CTA offers Facilitation, Mediation, and Adjudication. While the first two are voluntary and somewhat informal, the final one puts the facts before the CTA for a binding decision. And it looks like the CTA hasn't accepted the airline's unsubstantiated excuses for delays.
(Mods, feel free to delete if my post is misplaced)