We did the Cabot Trail on a bus (well, ‘motorcoach’) – and I would not recommend that to anyone…
The shoreline is beautiful. In a car, on your own, where you can stop and enjoy the scenery, it could be a nice trip.
In a bus, trying to take pictures through bouncing/swaying tinted glass, it was really disappointing. The tour guide on the bus was great and told some good stories, but 10hrs on a bus was awful.