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;
Oh yeah…and a Jack Russell Terrier would make a great Emperor Palpatine! That breed is smart and can manipulate humans well. If Vader “a pit bull” could be easily influenced by a Jack Russell Terrier, anyone can