Prince Edward Island is rural, so people pick you up if you look like their neighbour's daughter who needs some help. Main roads (basically route 1 and 2) are easy to hitch on. Everywhere else, be sure to know where you're going, and use a sign with your direction on it. There's significantly more traffic in the summer; however, tourists rarely pick up hitchhikers. Getting to Charlottetown, to the ferries or to Confederation Bridge is no problem - from wherever. Getting to just any beach works fine, as well.
User:Baribeaup hitched from the Pictou ferry terminal to Charlottetown in July 2017. It didn't go well. Rides were often traveling very short distances, traffic was minimal outside of ferry arrival times, and ferry passengers were unwilling to stop. It's recommended to try to catch a lift while still aboard the ferry, and to use a sign with a destination ("UPEI" ultimately worked within a few minutes) when on the side of the road.