This is annoying I agree. I wrote to them and rec'd this reply.

We are targetting Mobile Flight Pass to be back online in late March. We apologize for the delay.

Regards,
Air Canada Mobile Team

Why do they say "back online"?
The flight pass feature has never worked or been online.

Also why give the following prompt " undergoing maintenance ". How can you "maintain" something that was never working in the first place?

Mobile Flight Pass is currently undergoing maintenance.
L'application mobile de la Passe de vols est présentement en période d'entretien.

I think the AC app is a great idea, just very disappointed that almost a year later the flight pass feature still does not work.