I simple Google search of 'Samurai Nintendo' didn't give me much. X_<
You know, I'd like to think I do have a fairly decent knowledge of Nintendo's first-party titles, Japanese included, and I can't really think of any major samurai characters, which is sort of surprising. I mean, maybe there was some sort of side-character samurai in a game like, I don't know, Eternal Darkness (there wasn't), but if that's the case, then more than likely it wouldn't be included in Brawl based on its popularity.
That being said, I just thought of a character that will probably make it: Custom Robo Robot. I'm sure someone's thought about that before, it's probably already been discussed, but I really think that it would have a shot. Especially considering that series is very popular in Japan, and pseudo-popular in America, too.
~Dac
Edit: Holy cheesy butt-nuggets, you don't need to be mean, dude. It was a simple question. And I'm going to laugh my a.s.s off if there's a Nintendo Samurai game announced at E3. Oh wait -
http://en.wikipedia.org/wiki/Sengoku_Musou_Wave
Samurai Slash FTW.
Edit^2: What's a Samuria? Sounds like a flower of some sort...