It was the easiest way for many years but Tyler reported a while back that that bus has been discontinued for the most part. It does apparently run still after later shows if the MK has closed.
You can also take the ferry, boat launch or monorail to the MK and take the FW boat from there.
Many, many years ago there WAS a boat that went from the Polynesian to FW in the evening for the Hoop. It was fun to take.
I have never seen a bus to the Polynesian from FW though. Just the one to TTC. But there is usually a cast member around the bus stop who can answer any questions. Things do change.