Doesn't work. We actually ran into an almost identical situation a few years back. I booked a B2B - Boston > Quebec City and Quebec City to New York (with out TA). The first leg had an overnight in Quebec City. A few days after booking, the "powers" at the cruiseline cancelled the booking. I asked about the possibility of spending the night off the ship (taking luggage and all) and then re-boarding as a new passenger. Answer came back ... a big "NO".
Either of these legs are perfectly legal by themselves ... but together they violate the PVSA (which, IMHO, needs to be updated or eliminated).
maggie777 - A LOT of the lower tier Azamara phone agents won't be familiar with this restriction and you probably won't get accurate information ... be skeptical if you get a positive response.