There are so many questions that only you have the answer to: Just the 2 of you, or additional family? Active or relaxing? Like or allergic to crowds? Do you want to be “entertained” or prefer to make your own?
I would never have imagined enjoying “cruising” but was pleasantly surprised, partly due to the range of services offered.
I was able to spend most of my sea days reading anti socially while Jane made new friends, and then argue with them later over cocktails! The food was always great and the option of Black Tie and Gown Formal Nights added a little romantic touch (I look hot in a Gown!) and on port days there are excisions and activities for all tastes.
Royal Caribbean has an itinery that visits most the places you mentioned (except Cuba) on a cruise that includes Belize, but wherever you choose, the vacation will be enjoyed more based on the company than the location.