The Grand Floridian is in the Magic Kingdom area facing the Seven Seas Lagoon. From it you can access the Magic Kingdom as well as Epcot by monorail .
The Boardwalk is located just outside Epcot's World Showcase and has convenient access to Epcot and Disney MGM Studios by either walking (Epcot is about 7 minutes and the Studios is about a 15-20 minute walk) or boat ride.
Neither resorts are very close to the other. You would need to take either bus transportation from the Boardwalk Inn or the monorail via Epcot's front entrance.
Hope this helps.