Along with young Ali, Tunney is the classic heavy that may just be the worst matchup for Sonny. I think Gene frustrates and out points him. Just doesn't cut the ring off well enough or have the quickness (of hand or foot) to track Tunney down.
Gene frustrates him for some rounds but Liston catches up via the jab... especially if planned for the longer route.
I could see Tunney winning some rounds on skill and heart, but I don't think he would be strong enough to last he distance. Liston KO 9
I think Tunney would make it competitive and last the distance. If he's able to make Sonny angry, thing's could get really interesting. I'd pick Liston by decision in the end.