When AC re-configured the CRAs and made them CR9s, they added a second large closet up front to store bags. I don't ever remember being required to check my roll-aboard in J before that, and certainly it's not required now. Although many FAs don't seem to understand how to load it properly and sometimes a bit of Tetris is required to get things to fit.

Also note that AC does gate check slightly differently than US airlines. On UA and DL's CRx planes (although I don't believe UA has CR9s, only CR7s and CRJs), it's standard to check bags on the jetbridge and return them on the jetbridge at arrival. AC refers to this as "sky check" and typically only offers it on short flights on smaller planes, e.g. DH3 YCD-YVR, DH4 YTZ-YUL, etc. It's rarely, if ever, offered on a CR9. When AC refers to "gate check", they are talking about checking your bag to its final destination, to be picked up at the baggage carousel with regular checked luggage.

That won't be an issue for you flying J on the CR9, but for reference just in case it's applicable on another flight