I've spent a fair bit of time kicking around Maine islands over the years, which are a lot more likely to have random visitors. One really weird phenomenon is that locked cabins tend to have more vandalism problems than unlocked cabins with a guestbook for visitors. I've never quite figured out what this says about human nature.

Maine's liability laws are excellent. They basically say, "So you hurt yourself? And you were wandering around the woods? What part of 'woods' didn't you understand?" So the social conventions in rural Maine provide a certain freedom to wander around unoccupied woodland as long as you don't make a nuisance of yourself. Posting your woodland against trespassing was historically considered a bit anti-social in a lot of places.

Nova Scotia appears to have relatively sane rules for liability in wilderness areas: http://nslegislature.ca/legc/statutes/occupier.htm I'd guess that your island probably falls under some combination of 6.1(c) or (d), but it's probably worth asking an actual lawyer.

Have fun with your island! And pay attention to the SAR folks—living on an island is only slightly more dangerous than living anywhere else, but when bad stuff happens, your options may be worse. My childhood best friend once had to make an hour lobster-boat ride with a stick jammed into his throat just below the jaw bone. This experience put an end to his family's island living. Your biggest risk is probably making that 5-minute boat ride in a bad storm.