If you board the Monorail at the Magic Kingdom to visit the Grand Floridian you will need to take the Resort Monorail (toward the left) at the Magic Kingdom Station. The resort monorail travels clockwise meaning the first stop will be the CR.,TTC, Poly and then the Grand Floridian. If you want to visit the Polynesian just jump off the monorail at the Poly before visiting the Grand Floridian, then you can get back on the monorail from the Poly to continue your ride to the Grand Floridian. Once your at the GF you could walk to the Poly (under a mile) or you could ride on one of the Resort boats back over.
Have a Great Trip.