James Toney hands down. Cerdan was an aggressive swarmer which is exactly the type of fighter that a counter puncher like Toney excels against. Cerdan can't hurt Toney.
Sorry but I just don't see it as a 50/50 fight if Cerdan is in with the guy that beat Nunn and McCallum at 160. Cerdan's best win was against Zale but keep in mind that was the last fight of Zale's career and he has over 80 fights on his odometer at that point. A lot of Cerdan's record was built up against inferior opponents in Europe. Don't get me wrong, he was a great pressure fighter but the only way I see him beating Toney is if Toney is less than 100% and struggling to make weight. I'm assuming these mythical matchups are the best versions of the two fighter's. If that is the case, it's no contest. Toney was the superior fighter. Anyone can see that by just watching film of both.
Toney has to be the favourite here based on styles, although given how inconsistent he was when it came to training, if Cerdan caught him on the right night he could easily win. Cerdan wasn't the kind of guy you could afford to take lightly. But both at their best, Cerdan's swarming style plays right into Toney's hands.
Toney had several fights where he looked ordinary or at least had major troubles against pressure fighters or skilled fighters who played the role of aggressor. It wasn't just the Tiberi fight. Hell, watch him against Merqui Sosa, who didn't have 10% of the technical acumen Cerdan did (granted, that awkwardness was a part of what made him so difficult). This "Toney whoops anyone that comes to him" mentality is more theory based than reality based. Or else you guys are only remembering the good times.
Nunn was breaking down in that fight. Toney was behind on the cards but breaking him down. McCallum was not at his best but still ended up winning a light heavyweight belt against a tough Jeff Harding a full three years after fighting Toney in 91'. Cerdan was a tough guy no doubt but I question his greatness when looking at his record and also taken into account that he fought in the same day era and was a small middleweight unlike Toney who was a stout and stocky guy that was able to fight all the way up to heavyweight and be more than competitive. I'm not knocking Cerdan but I don't see him on Toney's level. In 30 years as a pro, no one ever KOed Toney and that includes heavyweights. Cerdan's only chance is outwork a weight drained Toney but again, if we are talking the best versions of both fighter's it is no contest. Toney was faster, stronger, hit harder, tougher, better defensively etc. The only thing Cerdan did better was pick up women.