The Boardwalk is not really within walking distance of CBR. But you can easily walk there from Epcot's World Showcase, exiting at the "International Gateway" between England and France. When the path branches, it is the Beach Club that is sorta straight ahead / on the right and The Boardwalk is over on the left.
Or you can get on the boat, at the same International Gateway exit. It stops at the Boardwalk and may even be faster than walking.
The only place you can walk to from CBR is Pop Century. You even need to be careful walking there since you have to cross a road that is probably a serivce access road. The Boardwalk is within very close driving distance of CBR.
No there is no safe way to walk to the Beach Club. There are ways you can do it but most people aren't expecting to see someone walking and it could be dangerous.