Neither a Disney hotel or a port hotel are going to guarantee early check in unless you pay for the night before. You can call ahead and request early check in and they usually will if the room is available. You generally can't be picky on room. If I am trying to check in early, I usually say I will take the first room available. If you need some specialty room or have lots of requests then your room may not be available till the stated check in time.
As others have said, if you show up early they will let you store your luggage and enjoy the amenities of the hotel till your room is ready. I would just pack a day bag with anything you may need for the first half of the day.