Spoke to a WJ agent. They're only allowing free cancellations on flights between May 15 - 21. Our flight is May 23 so we'll have to wait til possibly 19th for them to allow cancellation at which time AC flight prices will probably skyrocket.
The other angle they mentioned is not all flights will be affected - some pilots will inevitably cross the picket line and certain flights will go ahead as scheduled. Nobody knows which ones will go ahead but I'm hoping international departures have priority. If and when a strike is announced they'll potentially know how many pilots are available for the upcoming week and be able to announce which flights will go ahead and which are grounded for the upcoming week. Forced to take a wait and see approach for now.