"Real Bretons" are French. You know that, right?
Depends on who you ask. The French government does not recognize Breton as a nationality, nor Breton as an official language (it is the only surviving Celtic language to be denied recognition). Nonetheless, there are a few hundred thousand people who describe themselves as Breton and speak Breton, there is a Breton flag, a Breton national anthem, a Breton chivalric order, a distinctly Breton flavor of Roman Catholicism, Breton nationalist political parties (of limited support and no real power), and most of the other trappings of a staunchly (but peacefully) held nationality.
Back on topic, I'd expect a distinct regionalism within High Rock, as it had been for most of its history a divided and quarrelsome province. This should be especially true of the Reachmen, who might show coincidental commonalities with real-world geographically isolated peoples such as Highlanders or Overmountain men.