Two of my favourites. We would see two great fights. My money would be on Sugar Ray as long he fights his own fight and not get suckered in by 'The Kid' to fighting his. I envisage two close decisions going to Leonard. And yes I agree with McGrain that these two are the second and third best welters of all time.
Leonard was probably the slightly more skilled and pleasing to watch of the two with their overall generic physical talent being six and half a dozen. Leonard a shade quicker and clearly harder hitter but Gavilan with the better chin and brawling capabilities and more at home naturally fighting going backwards. Leonard could get home by either a very close or clear margin and neither would shock me. Nor Gavilan getting the nod. My underlying faint concern for Ray would be that his best and most natural approach - cultured aggressive box-punching on the front foot - would play into Gavilan's hands somewhat. The approach for Leonard that I just mentioned was probably Robinson's best manner of fighting, and he had a level of doglike nastiness and power that Leonard couldn't quite match despite being quicker. And even Robinson, a physical monster at 147, was forced into taking a more calculated approach at range to gain the edge over Gavilan. Even Basilio couldn't outslug him - I doubt anyone could in and around welter. In that case, it's not hard to see Leonard being forced to take the approach he took vs Hagler and Duran the second time. His two most famous wins, but a bit atypical of his career in general and not how he usually operated. Both wins also marked by Hagler being a dimwit and Duran an out of shape spiteful child. That said, Leonard even when flurrying and shoeshining on the move was unusually good at knowing what judges wanted to see, and when. A master at swaying close rounds to his advantage that he might have otherwise been losing. Easy to see him shrewdly gaining favour on the cards that way if plan A doesn't go exactly as planned. Hard fight to gauge imo. I'd probably shade towards Leonard at a guess though.