We flew to Montreal 2 months back. We only needed to show rabies certificates but carried all our cats’ paperwork as well. Make sure to call the airline (in our case it was Air Canada) to book a pet in cabin. You’ll also have to check in at the counter (and not online) on the day of your flight. Most flights can only accommodate 3-4 pets per flight so you’ll definitely need to call and book your flight in advance so they can ensure there is space for your pet.
Even though we’d booked 2 pets in cabin, Air Canada messed up! We got to the check-in counter and they said they could see only one of our pets registered when we had proof that we had registered for 2. They were really difficult to deal with but luckily there were probably not many other pets on flight so we paid the extra 50$ for another cat to come in with us. Definitely confirm that your pet is registered the day before your flight as well!