It would be a pretty long walk to the MK, and I do not think that there is a path all the way to the MK.
The best way to get to the MK from the Poly would be the monorail. From the poly the next stop is the GF then the MK. Returning from the MK it goes to the Contemp and then the TTC and then to the Poly.
There is also a boat that goes from the Poly to the MK, I think it goes from the Poly to the GF and then MK.