I got back from a similar trip a couple of weeks ago. I crossed the border at Ogdensburg and headed southeast through NY to Queensbury, then over to Concord, NH (10 hours riding time on the first day). If I were to do it again, I'd spend quite a bit more time to explore on this segment of the trip. All the roads I took were very lightly traveled and in good shape.
Second day was another 10 hours to Amherst, NS. I do not recommend taking the #1 through Maine - it was nice and scenic along the coast, but it was also rammed full of vacation/cottage traffic and road construction.
I came back through NB and Quebec, but only because I didn't want to be traveling through the states on the July 4th weekend. Maybe it is because I've done this route many times in a car, but I can't recommend it unless you're making the effort to do Gaspe. The highway is just mind numbing. Going through the states gives you many more options to hop off the highway when you get bored, and then to hop back on when you want to put on some miles.
If you are worried about road conditions, you should prepare yourself for NB and NS. The secondary roads between population centres are generally pretty good, but the less used ones can be in truly awful shape. I enjoyed these roads on the bike since they are almost completely empty of traffic, and part of the fun is avoiding the potholes, but I can see how that would not be everyone's cup of tea. Driving a car on them can be miserable since you can't weave your way through the holes like on a bike.