Thanks everyone for the replies. Although it may be a bit risky, it sounds like 40 minutes is doable at ZRH. I hope everything goes smoothly. My final destination is in the U.S., but United showed availability only via YYZ at the time of booking, so I took it. If I miss the AC flight, hopefully they can rebook me via Canada or straight to the U.S.

Taking a later flight is an inconvenience. But, I'm going home and I have an extra day off. Also, spending some time in Zurich (which I've never been to) doesn't sound bad.