According to the BBC news report, Peter Mayhew's casting as Chewbacca was something of a happy accident. Dave Prowse was apparently originally down to play him, but he wanted to play Darth Vader instead. Peter was cast fairly late, based on his stature, before going on to make the character well and truly his own.
It makes me wonder if, had the original casting stood, Chewie might have ended up with a Cornish accent? (Prowse was dubbed as Vader - "Luke, oye am yurr farther!")
