Listing on Air Canada ?

Hi - Hoping to travel LHR-YYC on a ZED ticket on Monday. Does anyone know if it is mandatory to "list" for Air Canada.
Thanks a lot.

I know it's mandatory for employees but no idea about others... What ended up happening?

They told us at check in we should have listed, but we managed to get the last couple of seats anyway. I've now listed for our return!