Thought I’d provide an update:

Outbound LGA-YUL was smooth, half empty J cabin. Upon boarding, FA offered to stow my carry on (and that of most J pax) in the closet.

Inbound however, not so smooth.
I was waiting in the group 1/2 lane shortly before boarding began, when the GA came up to me and asked me to check in my carry on. I told him I’m in business class, and he then said “unfortunately you have too many bags, this is a small plane. Here’s what we’ll do, I’ll check your carry on and you can hold onto your backpack.” Like he was doing me a favor LOL
I only had a backpack and carry on anyway, so I did not “have too many bags.” I shut him down real quick and said I’m not checking it in, I’m in business class and will put in the closet if it doesn’t fit in the OH. He finally relented and said, “ok you can try.” And FWIW, I was the 2nd pax to board. Is it standard for them to ask J pax to check in their bags before Y pax??
Boarded and asked the FA if I can put in closet (which was closed) He told me try the OH first. Of course it didn’t fit, so I had to swim back upstream and he finally opened the closet and let me put my carry on in there (while not looking very happy about it)

So what gives here? Is it always such a pain? First and last trip on AC CR9 if I can help it

Edit: I’ll give credit where it’s due, the fact that AC offers a hot breakfast on a 55 min regional jet flight is quite impressive. AA, UA, or DL would never