My friends just returned back from those Maritime Provinces. They took around 10 days. They have 6 people and rent a mini-van. Actually what kind of vehicle you need will depend on the number of people joining and how many stuffs you are going to carry on? I believe all cars from a renting company is very reliable.
BTW, I have a national park & national historic site pass for transfering. If you have a plan to those Maritime Provinces. I believe you'd better to have it for a group (up to 7 people).