As a student of the cruiserweight division, I can emphatically state that only Magne Havnå would have a real chance of defeating Marciano.
Holyfield would be tough,Evander reminds me of Ezzard Charles a little....Spinx would lose,Toney would be good but the pace and pressure would get to him,Qauwi would get stopped.....Rocky would have been a very successful cruiser,which essentially he was.
When Holyfield was coming up he was often compared to Ezzard Charles. Did not become as great, all those steroids and bodybuilding ruined him. He had big wins as heavy, but a lot of losses too, and some weird performances (where he suddenly just could not punch or move, Bowe 3, Moorer fight, Toney bout)
Marciano would imo beat the lot with Holy giving him the toughest fight, but I like Marciano, likely by stoppage over 15. Haye? Haye woul d **** himself against Marciano the way he did against Wlad - he's not brave enough to do what he would have to do to have any chance of winning and would take no chances, he would just box to survive. Marciano is a different breed of man to Haye.