Holland America does this route.
It is funny because I had also always wanted to take one of these curises, but we found that the best part was seeing Quebec, and the time on the St. Lawrence, which we envisioned as being alive with fiery fall colors, was so wide that we could barely see the shore.
Stopping in Maine was fun, and Boston - but all in all I now think I would rather see those cities by car and maybe skip the cruise - UNLESS ITS A REALLY GOOD DEAL.
If you do go - do some research and try to time it for peak fall folliage. I think our cruise was a little too early (still lots of green out there) - but then again, that changes every year so you really never know.