If you are talking about Seaworld in Orlando, it is quite a distance. Taxi would be expensive and maybe even hard to find to go that far. Also, you need to be aware of how much time you have. If you are there the day before your cruise, maybe rent a car instead. But, wouldn't you be flying into Orlando anyway? Why not stay there?
Please do't take my word on this, since I am not into amusement parks ('tho Seaworld is the best to me). Do a bit of research.
Thank you very much for your reply. Yes, I am talking about Seaworld in Orlando. We have one full day in Orlando as part of our Florida/Bahamas cruise and I was hoping to get a taxi instead of using the NCL shore excursion because I wanted the ability to leave earlier if my younger daughter gets restless (she's 2).