A clarification...last time I was in Portsmith, NH there was a ferry that went to Nova Scotia on a regular schedule that was called (if I remember correctly), the Scotia Prince. That was a few years ago now, so maybe things have changed.
Lloyd, I took that ferry, from Portland ME to NS in the late 1990's. Was an overnight trip. Departed around 9:00 pm and arrived in NS about 6:30 am. My wife and I had a cabin.
That service went down at some point as was recently replaced by a new, much faster boat. 5 hour trip departing at 8:30 am. This new service ( 4-5 years old I think) also sails out of Portland ME.