Direct bus to the Magic Kingdom, then transfer to the resort monorail to the Polynesian. This works during MK operating hours, of course. After then, you'll need to change buses someplace else, either Epcot or the Marketplace.
I agree with DC7800.
That's how we did it when we stayed at AKL (which is an AWESOME hotel), and it worked out very well. No matter what hotel we stay at, we never miss an opportunity to eat at O'Hana!
Barb
Visit the Platinum Castaway Club at: www.castawayclub.com