Woahhzz thinks the match is in Leixia's favor. I honestly don't believe Viola has any matchup inherently in her favor (only that her pressure game and damage off of 3b and 44a can makeup for a bunch of stuff), except maybe Ivy and/or Ast...but I'll admit I haven't gotten to play the former enough to say. Viola's speed is pretty average, all of her stepkill requires her to be in just about breathing range (outside of 66a and 22a+b), her body is pretty much her hitbox and hurtbox on all of her attack, she has mediocre range, and she can't punish worth a shit.
I also think that Nightmare, Cervy, and Mits kill her (also theoretically oPyr...but haven't gotten to test that enough). I would also say Natsu but I only have my matches vs. Hawkeye to base that off of, so I can't really say. I've only gotten to play vs. Thugish's Leixia once with Viola (and he doesn't know her well) so I also have nothing to base that off of.
Theoretically, it should be a very hard match for Viola, as Leixia has everything she needs to be a problem vs. her...but, like I said...I don't think many matches are in Viola's favor...just that her pressure can make up for them.