As much as I love dogs, I don’t know many breeds. I suppose the obvious choice for Vader would be something big, dark, and intimidating like a Rottweiler, Mastiff or Pitbull. Newfoundland is another possibility, just for their immense size.
I could see Leia as a French bulldog, for obvious reasons;
Cool choices! If Leia’s a Frenchie, Luke would have to be one too. I think Yoda would be a great Chihuahua because of those massive ears, and I see Chewie as a sheep dog because of all the fur!