Make thorough backup plans for any kind of weather problems such as low visibility or high winds. Always have a place to land and stay over.
Make sure your emergency locator thingy is new and working.
Have a small survival kit which includes matches.
Make sure you have a backup radio and GPS.
Personally, if I was flying over the Bay of Fundy I would bring a size A or B oxygen tank and fly at 15,000 feet during the middle part. If you do that, you can pretty much stay within gliding distance of land the whole way. (You know the best glide speed of both aircraft, right?)
By the way, the neck off St. Mary's Bay looks pretty bad for off-field landings so you definitely want to pick a spot beforehand.
...and remember, the engine always runs rougher over water :-)