At Shediac there are two marinas Point de Chene Marina (www.pcyc-nb.ca ph. 506 532 6800) and Shediac Marina ( www.shediacbayyachtclub.ca ph.506 532 7007) that may be able to help. You might also consider the Charlottetown Yacht Club on PEI. It's near an airport. Also it's not much further to the Bras D'Or lakes and there are two marinas (www.dbmarina.com) there and you could rent a car or take the bus to Halifax. I've never dealt with any of these places personally but have friends who keep their boats in Shediac without complaint. The spots in Bras D'or have a good reputation and deal with a lot of US visitors so should be able to answer your questions. Let me know if you need and other info.
David