Abe Attell basically laughed when asked about this pairing and his job was boosting Marcel at the time.
Cerdan remains under rated, perhaps because he's not a media guy often shown. I think this match up would produce a lot of action. Cerdan was an aggressive power hitter, but he also had a good defense. Greb a windmill attacker, without the punch but with plenty of stamina and durability. Under 10, Greb. 15 SD either way.
Logically you've got to favor Greb, but Cerdan looks very, very good on film. In my opinion, he looks better than just about any of his contemporaries or near-contemporaries.