I think all fights would be competitive.
He'd likely beat a Duran. Call me crazy, but i think he would be able to ko Hearns. He has the style to slip punches and take Hearns out on the inside.
I'd favor Hagler slightly, in a brutal technical slugfest simply because canelo has shown to gas late. Canelo winning isn't out of the question, though.
Based on style alone, id say Sugar Ray would do best against canelo. Leonard has the feet to give Canelo serious problems.
Historically, Canelo has struggled most against slick boxers(lara, floyd, trout). Leonard was one of the slickest of his time.
All that said, we are comparing the complete careers of 4 fighters to the career of a fighter who is literally in his prime. Canelo has plenty more to give. Things could change as Canelo's career progresses.