2 years ago I had to go via Montreal on a trip from NL to middle east (it's SO annoying to spend all that time flying west to have to fly east!), and had 1 hr connection time, but the customs part was London, and I had no problems.
Last year going to WDW, my flight from NL was via Montreal, with just 1 hr connection... and customs. That had me concerned, but the booking agent at AC said it was no problem. I did pack my carryon with enough to get me by a couple days (in fact, most of my clothes & shoes!).
As luck would have it, weather somehere (this was mid Sep) resulted in my flight being cancelled.
I managed to rebook to go via Toronto, with a 3 hr delay.
And was I glad for the 3 hrs! A loong wait to reclaim the baggage, then a loong lineup to get in to the customs section. I was bringing NovaScotian apples with me so had to go thru the section for people with things to declare (that was the quickest section of all).
This year I had the choice of 1 hr or 3 hr connections in Mtl or TO, and I didn't hestitate to take the longer wait time.
I wasn't as concerned as making there with my luggage as I was about being sure I made my connections.
If I could travel with just carryons, I might consider the 1 hr connection, but man, that's stress I don't need!

But it is a common connection time, and if (in today's travel/security climate) it didn't work most of the time, I feel AirCanada would have changed it by now.