Starting at the GF, it's a nice walk over to the Polynesian. From the Polynesian you can walk to the Ticket & Transportation Center. Exiting the Magic Kingdom at Main Street, you can walk to your left to the Contemporary. There is a pathway by the resort boat dock that appears as though it will take you to the GF, but as the above poster mentioned, you only make it as far as a canal and then you have to turn back. I believe the canal is where they store the boats for the nightly Electric Water Parade and that's where they enter and exit the lagoon.
Short answer to your question is no. You cannot walk around the Seven Seas lagoon and you cannot walk from the GF to the Contemporary. Only GF to Poly to TTC or Cont to MK.