Hello
disclaimer : I am not a AMM/RJ expert but was in AMM very recently. I believe it is feasible but very risky. You will likely have to go through security in AMM. If you misconnect, it will mean waiting for the next day (providing RJ has a daily flight to YUL). Personally, I would not risk it.

Otherwise, the best option from BEY to YUL is definitely via CDG with AF or ME on BEY-CDG and AF on CDG-YUL. There are always tons of Lebanese people on AF YUL flights. Multiple flights on both sectors (AF and ME have 3 or 4 daily BEY-CDG) and AF has 3 daily CDG-YUL so plenty of connection possibilities and rebooking options in case of misconnection. In case this could interest you, AF now flies also to YQB (Québec city) 3x/weekly.