I'm speculating based on what Tim said in the live. He specifically mentioned that J$ was tall enough to ride the Aqua DUCK, which is on the Fantasy and the Dream. The Aqua Mouse is on the Wish.
He also mentioned portS when talking about not having shore excursions and just getting off the ship and maybe just exploring the port area. I think if they were going to Nassau, he wouldn't have mentioned that at all. Poor Deezy or whatever his name is.
The Magic is currently sailing out of Miami and this weekend's cruise is a 3 night Nassau/Castaway Cay. I do not think they would drive all the way to Miami with an infant and a (not) toddler to do the same 3 night on an "old" ship that they could take on the amazing and wonderful brand spanking new Wish for the same itinerary.
The Wonder just entered dry dock in Vancouver and the Dream is sailing back to NY from Europe this week.
I might be wrong, but my money is on Saturday's Fantasy. And yes, I know I'm weird that I keep up with such things.