Johnson I think. Alvarez is a very, very good fighter but a tad unproven at 175 (Kovalev was at the end of his rope when he met Canelo). Marvin was a very tough and dangerous fighter. A hard punching, reasonably skilled southpaw with a decent size advantage. I’ll give him the edge here but Canelos story isn’t written just yet.
Marvin Johnson is an aggressive southpaw that operates off of a solid right jab, but he was a good body puncher, always coming forward, remember the way he kept coming in on WBC Champion Mate Parlov on Dec 2 1978, Parlov could not deal with that constant pressure, stopping him in round 10, in a battle of southpaws. He later dueled with Matthew Saad Muhammad on April 22 1979, in a battle, losing by TKO 8. On Nov 30 1979, he engaged in a battle with WBA Champion Victor Galindez, stopping Victor in round 11, breaking Galindez's jaw in the process. Saul Canelo Alvarez, though a good boxer would not be able to withstand the constant pressure put on him by Johnson, who would utilize his right jab to set up very wicked body punches. Canelo would do an imitation of Billy Joe Saunders the other night, remaining on his stool in round 8.