How does lounge access work on an Aeroplan reward flight if the flight includes a plane that has business class and economy segments?

i.e. biz class flight on any *A carrier into YUL and then a short hop from YUL to YTZ on AC - like let's say FRA-YUL-YTZ or ZRH-YUL-YTZ

Does YUL have an arrivals lounge I can use during the layover? Am I able to get in having arrived on a flight using a business class reward knowing the final segment is AC's little props that fly to YTZ?

I may be new to FT (1st post actually), but I have been scouring the forums for months learning a lot already.