Thanks for the additional input everyone.
I was looking at the possible routings, and other than the non-stop flights, there are a few connecting flights that go through DEN.
YYZ-DEN is AC metal (A319), but DEN-IAH is on UA metal, which led to another question:
If I purchase a ticket on AC.com and my flight is a connecting flight where one segment is on AC metal and the other on non-AC, can I only upgrade the segment on AC metal, or can I somehow use my upgrade credits for the non-AC segment as well since the ticket was purchased through Air Canada?
Thanks again-