These match ups are over 15 rounds by the way.

Carlos Monzon vs Marvin Hagler = Hagler by close UD.
Carlos Monzon vs Roy Jones Jr = Jones by UD.
Carlos Monzon vs Thomas Hearns = Monzon by come from behind late TKO.
Carlos Monzon vs Nigel Benn = Monzon by mid round TKO
Carlos Monzon vs Chris Eubank = Monzon by UD.
Carlos Monzon vs Sugar Ray Robinson = Robinson by UD.
Carlos Monzon vs Sugar Ray Leonard = Leonard by UD.
Carlos Monzon vs Bernard Hopkins = Draw.
Carlos Monzon vs Julian Jackson = Monzon by mid round TKO.
Carlos Monzon vs Kelly Pavlik = Monzon by late TKO
Carlos Monzon vs Michael Nunn = Monzon by late TKO.
Carlos Monzon vs Mike McCallum = Draw.
Carlos Monzon vs Jake Lamotta = Monzon by UD.

Thats 13 match ups i have Monzon at 7-4-2, i think because Monzon was kinda slow hand speed wise and foot speed wise that he would struggle with movers like Jones, Leonard, Robinson, thats why i think he loses to those fighters, and as for Hagler i think the younger version of Hagler who moved well and counter punched could of beat Monzon as well. But other than that i think Monzon could beat the others on any given day, but fighters like Hopkins, McCallum, who are good all rounders is a very tough pick, thats why i have those fights as draw. Those fighters were just off the top of my head if i have forgotten any other fighters let me know and i'll add them to the list.