I really thing reservations depend on where you are. If you plan on going to somewhere like Acadia NP/Bar Harbor... big tourist area, I would make reservations, but you can still do an open schedule with a few key scheduled stops.
Re Eastern Canada, just a few thoughts:
Quebec: most of Quebec around the Quebec City to Montreal to Ontario along the St Lawrence River is like Ohio or Michigan but in French. This area somewhat flat and is more urban/suburban with lots of English speakers. If you go further east to Gaspe or further north you will find fewer people who speak English and may have some trouble communicating especially in smaller towns. Quebec city is worth a stop if you end up in the area, the old city has old world architecture and charm, like a visit to Europe.
The Atlantic Provinces: I would consider adding PEI onto your list (but add PEI National Park to the list of stops you may want to have a reservation for). PEI is really unlike anywhere else that I have been in North America, it is like going back in time. I would also add Cape Breton in Nova Scotia to the list if you are in the area, it is worth the drive.
