Masaki, I guess it depends on what you want to do with your time, and the availability of good guides.

Are there guides in Quebec that come highly recommended? What sights do you want to take in? It's a pretty compact city, great for walking, but if you want to go up the river, for instance, then it might make sense. Guides can also tell you lots of great stuff that you would never know, so if you don't have a lot of time to study guidebooks, it might be a good bet--I'm sure you would learn lots about Quebec culture quickly! But it really depends on the guide.

As for Bar Harbor, again, what do you want to accomplish? The town itself is tiny, as I remember, but it's the park you probably want to see. Again, if you can get a good guide, then probably it's a good bet. I think I might just rent a car and do the loop. It's beautiful, for sure, but maybe a guide could take you to special places you might not go, and being driven up Cadillac Mountain would be better than having to do it yourself (hair-raising switchbacks).