We made the trip last summer with a 34 foot gas class A towing a Honda CRV
Note that I am talking about two different ferry crossings here
The Marine Atlantic ferry from Sidney Nova Scotia to Port a Basques Newfoundland is big. It has 3 vehicle decks and it feels more like parking in a large football field ( with a roof ) than a ship. I can’t see any problems here.
We also took the trip from St Barbe Newfoundland to Blanc Sablon Labrador just to say we went to Labrador. This is a smaller, single vehicle deck ship. Still has room for plenty of semi trucks. The man directing the loading looked at our motor home and said “ If you don’t stay RIGHT BEHIND that truck, you wont get on. “ It was a big gasoline tanker trailer and as I closely followed 10 feet behind him I got to read all the safety and warning labels on the back of the tank.
Coming back to Newfoundland from Labrador they did not say anything, so it may be tide and load conditions that change the ramp to boat angle.
If you take this part of the trip, this ferry may be the one to watch. The loadmaster knows what he is doing, and he does not want a hung up RV blocking his ramp. However he might not see something hanging down under the motorhome