My ds was 21 months for our first trip to WDW (and dd was 3 1/2yo). He LOVED disney - loved the characters (except the villians), loved every ride he was allowed to go on, enjoyed all the sights, shows, etc. We did the trip very slow, on the kids terms, had afternoon naps and lots of down time. It was an amazing trip and I'd do it again in a second! Can't speak for Hawaii or a cruise, but agree w/ others that the cruise wouldn't really be good, and the flight for hawaii might be an issue. And in hawaii, for your toddler, there's the beach and I don't think much more (right??)... you can get that at disney too (the beach club is the best resort for that, but others also have sand and pools - no lake swimming anywhere). The sand bottom pool at storm along bay at the beach club would definitely be just as much fun for a toddler as any beach would, plus you have all of disney too.
have fun whatever you decide!