it depends heavily on the shape of ruiz, if he is in his regular shape i think he can outbox hunter by beating him to the punch and smothering him with combinations. if he shows up as a blob, i think hunter has a decent chance of winning by sticking and moving, use the jab and any time ruiz tries to get close move and take the chance with an uppercut.
One of the many interesting matchups that could be made at heavyweight, but likely never will because fighters are being too cautiously matched these days.
Depends from a) motivated and well prepared Ruiz will show up. b) lazy version. Ruiz might come in at 260 lbs, might come in at 300+ lbs. If Ruiz is motivated and will train a lot and will be diligent, he might improve!
Hunter easily beat him in the amateurs though that was a long time ago but Hunter was a sparring partner for Ruiz for the Joshua rematch and he apparently was dominating Ruiz in sparring. Of course sparring is just sparring but Hunter's movement, work rate and durability pose real problems for Ruiz Jr. Hunter most likely wins a decision.