The problem with this is that AA and UA are in different terminals, so you will have to go from terminal 3 to terminal 1, which requires the use of the train. I think if everything is on time that it is doable, but tight, and will be especially tight if there are any delays, even more so if you have checked bags. I believe the cutoff time for checking in bags is one hour, which will eat into your connection time. Again doable if on time, but it doesn't leave a whole lot of room for error. Now if you don't have any checked bags and can check in online this will give you more wiggle room. Global entry/NEXUS will significantly speed up the process in Toronto as well (with NEXUS I've gotten from door to the other side of security and customs in under five minutes).