Shakur picks him apart. Ryan's a decent boxer with a nuke of a left hook, but Shakur is one of the most versatile and technical fighters in the sport and is a defensive wizard. At long range, Ryan can't win the jab joust since southpaws give him problems and Shakur understands how to win lead hand engagements, and in close, Shakur has an elite inside game and Ryan is really uncomfortable there, he doesn't know how to frame. I think Shakur puts on a 12 round clinic honestly.
Before they both last fought, I would've said Shakur easily. Now I have no idea but it'd be a huge fight. I usually always go with the boxer over the fighter so I'd give the edge to Shakur.
Shakur is better on the backfoot than Haney so Ryan wouldn't find it as easy to tag Shakur as he did against Haney. But it's hard to call because although Shakur passes the eye test, his level of opposition has been trash: shot Herring and B-level Valdez don't tell us much about how he would do against someone like Ryan. I think it would be a close decision either way, right now I'd slightly favour Ryan but I'm not convinced.
If Santos induced timidity in Stevenson, I can only imagine how much the pride of Newark would be on his bike against Garcia. Nevertheless, Stevenson is extremely elusive, and I can envision a scenario in which he frustrates Garica and earns an unsatisfying (for the fans) decision.
Shakur would do what he always does when facing a genuine threat; get on his bike and fight exceedingly negatively. He would likely take a decision but the fight would be atrocious to watch.