The buses start running every morning by 6:30..so if you decide to go the bus route, be out at the MK bus stop by 6:20. that way you'll be on the first bus.
But, here's the issue, the monorail doesn't start running until 7am. Even if you got on the first monorail run, at the MK, you wouldn't get to the Polynesian until 7:20ish.
If you mention that you need to get to the Polynesian for 7am, to the bus driver, you 'might' get lucky and he 'might' offer to drop you off at the Polynesian after he leaves the MK....maybe.
I would just take a cab over. Around 6:40ish, go to the Luggage Assistence desk or the front counter at your resort. Tell them you need a cab to get you over to the Polynesian. One of two things may happen. 1. they call you a cab or 2. they offer to drive you themselves! That has happened to me a few times. Just be sure to tip them heavily!!! I usually give them a $10 bill!