I went on a princess cruis in January to the same destinations. Even though it said the excursions were booked, i still went to the counter and they had availability. I went diving with the dolphins in Roatan at St. Anthony Keys. It was the most wonderful experience I have ever had! The people were friendly and great, they did a video of the dive and didn’t rape you on the price ($45), they allowed cameras where in Cozumel they did not and still wanted to charge you $130 for a disk of pictures. I hope you have a good experience with Princess, we did not. Take your own gear, don’t trust anyone elses. The rental gear I did see didn’t look all too great, with the exception of the Dolphin Dive in Roatan. Their gear seemed pretty decent. Hope this helps!