In about a month's time I'll be going to New York with my parents. We're flying via Canada both ways (because it was cheap... and I can indulge my inner plans enthusiast with some "fun size" planes on the hop across the border!). Am I right in thinking that this means we will go through US pre clearance at Montreal (in our case)? It's a through Air Canada flight with under 2 hours at Montreal, but I assume that takes into account going through pre clearance etc?
To provide an update on this, we (my parents and I) did this trip today. After arriving at Montreal, we followed the signs for connections. At some point in the arrivals corridor, connections are directed into an atrium, whilst everyone else carries on to (presumably) Canadian border checks. At this atrium, passengers connecting to other Canadian destinations go one way, whilst USA and international connections go another.
Following a rather convoluted path around the edges of the building, at some point international connections are siphoned off, and eventually USA passengers arrive at a small security check - standard procedures apply. (Interestingly, they wanted laptops (specifically) to be removed from bags. And also shoes off. I don't recall coming across either of these before, but I haven't really done that much travel and imagine this must be reasonably common in some areas.)
After security, you get deposited in a reasonably-sized US pre-clearance hall, which I assume also deals with "standard" passengers travelling to the US from Canada. And once through that, you're into the departure lounge. No Canadian immigration/customs/anything.
From the point where connections get separated from other arrivals, it took around 5 minutes to reach the security queue along the never ending corridor, 20 to get through security, and 15 to get past CBP. All fairly relaxed, no issues. They do like to scan onward boarding passes though as you make your way along the corridor - 5 times for us at different points!
So, in summary, a very pleasant, stress-free process, highly recommend (though whether that's also the case at other Canadian airports I don't know).
We then had a nice quick hop down to La Guardia on a CRJ900, including full 360° loop over Manhattan, which was nice (except I had a "window seat" that was missing said window...). Followed by the slightly odd experience (for us European travellers at least) of arrivals and departures mingling together in the terminal at La Guardia. Doesn't feel right!