From what you've told us, it sounds like you may have expected more than you should.
Under the Aeroplan rules in effect since November 2020, what you book is what you fly, unless you eUp or buy an upgrade.
So, if you're booked FCO-YUL- YYZ, with the first leg confirmed in business and the second in economy, that's what you'll fly, even if every business seat on YUL-YYZ is empty. Only under the pre-Nov-2020 rules would you have been waitlisted.
You mention having booked before dynamic pricing, I'm not sure what you meant by this? Or did all of this happen to you quite some time ago?