I wouldn’t pick many people to beat Canelo.
But Hagler was a dog, he had a lot of aggression and could push a pace that I don’t see Canelo being able to sustain. Styles make fights, and Marvin is a tough style to deal with. I think it would go somewhat similar to Hagler/SRR, except prime Hagler not an older Hagler. (And Canelo being Canelo...)
Both extremely durable, I don’t see anyone going to sleep.
I think Canelo has cleaner boxing, and he would certainly get his shots in, I could see him landing some very nice shots and winning some early rounds but Hagler had a hell of a chin and great cardio.
I think Hagler wins a decisive decision splitting the early rounds then taking over.