It will take your inbound aircraft almost 5 hours to get to Vegas from Toronto. You could follow an online flight tracker like Flight Aware and cancel online as soon as your inbound Westjet flight leaves Toronto. That should give you plenty of time. If you need to call and you're worried about being on hold forever and not getting through in time, call the morning of your travel day - or even the night before, since pilot strikes are usually well covered by media and you'll have more than just a few hours' notice.

Refunds aren't quick ... my experience (and limited to only a handful of occasions cancelling comfort fares during the worst of the pandemic) has been on average about 3 weeks to see the refund on your card. As always with AC, YMMV.