The ships change in April - they should have told you that. If you really want to go on Sunshine they might move your cruise to a few weeks earlier.
Personally, Sunshine is more interesting because it is new (madeover, anyway) and has all the funship 2.0 upgrades.
Carnival Dream is nice, but it is not a FunShip 2.0 ship. It also gets more complaints than a lot of Carnival ships because it is big and frankly crowded.
It is 6 of one, half dozen of the other, Dream is newer and bigger, Sunshine is just remodeled to make it a fully "up-to-date" Carnival ship.
I am guessing that you will have a good cruise no matter what, but if you really want to go on Sunshine see if you can move the cruise date. Did you go through a travel agent? (I hope)