Upvote:2
Unfortunately the answer is "you will probably make it" but you won't know before you get there. The minimum connection time for Canada to US for Montreal is 55 minutes. The airline determines this by monitoring the actual number of missed connections and dialing the time in so that this number is at some target. If they make it longer they will lose some passengers because of longer connection times and more attractive routes elsewhere, if they make it shorter they have to deal with more angry passengers and occasionally pay for hotel and food voucher. It's complicated trade off but clearly the target is not "zero".
55 minutes seems optimistic so there is a non-trivial chance that you will miss it. On my last AC flight I was going from the US to Europe via Ottawa. The min connection time for this is 60 minutes and there was absolutely no way, I would have made that. Even with the time that I had (90, I think) it was dicey and I had to beg my way through the immigration line. Fortunately the other people in line very nice enough to let me cut in.
Upvote:3
Air Canada publishes their estimated minimum connection times on their website and it seems that you'll have enough time !
The table for Canada to US transit states
Connecting through: | Minimum Connection Time Calgary | 50 min Edmonton | 50 min Halifax | 45 min Montreal | 55 min Ottawa | 50 min Quebec City | 30 min* Regina | 20 min Saint John, NB | 30 min Toronto | 1 h 10 min Vancouver | 1 h 10 min Winnipeg | 1 h 15 min Example: If you're travelling from Victoria to San Francisco with a connecting flight in Vancouver, you'll need to provide for a minimum connection time of 1 hour 10 min between your arrival in Vancouver and your departure for San Francisco. *15 minutes for connections between 2 Air Canada Express flights operated by Jazz
Once again, my personal experience with US pre-clearance in YUL was always fast, they have a lot of booths but I've never seen them all staffed.
The after Christmas period is usually a little calmer, so assuming there are no major snowstorms, you should be fine with the time you have.
I would confirm with Air Canada whether your bags will be checked through to the US, unloading at YUL can be slow and it might affect your ability to make it on time if you have to recheck. There's a small X-Ray right before the US customs for carry ons, but I don't remember any additional security beyond that.