Let's say Canelo does not beat Floyd, but does better than Cotto. Maybe somewhere near as good as Oscar and Castillo did. Who here expects Canelo's reputation to improve after Saturday night even with a loss? Or does he need a win against Floyd to improve his reputation?
In this case, I think a good showing will only improve his stock. The closer to controversial (a la Catillo/Hoya), the better (for his rep).
Of course a genuinely close loss will increase his rep because it will mean he will have done better than 95% of Mayweather's opponents and proved the majority of observers wrong (most think Mayweather wins a pretty easy decision). Close loss to Mayweather would be greater than anything else Canelo has achieved so far.