Hi, Sarah!
There is not a bus that travels between
Port Orleans Riverside and
Caribbean Beach. If you would like to visit one of these resorts while staying at another, you would need to transfer buses at one of the theme parks or Disney Springs.
While I love resort hopping to see what other resorts have to offer, hopping between these two resorts is a bit tough. Both are sprawling resorts, so the buses loop each resort at multiple stops. You really will be spending quite a lot of time sitting on a bus to do this. I suggest researching photos online, and enjoying your resort of choice. Then, look forward to staying at your second choice on your next magical vacation! (Yep, one trip is never enough to Walt Disney World!)
Resort hopping is usually easier for the Deluxe Resorts, as you can simply hop on the resort monorail to visit resorts near the Magic Kingdom, or for the Boardwalk area resorts, you can actually just walk to them from the International Gateway at
Epcot.
You have plenty of time until you need to book your 2018 vacation, so enjoy this time with some research, reading reviews. and looking over photos of each resort. Whichever resort you choose will truly be magical!
Cathy