Cotto and Marquez are both like 5'7 1/2. Khan is 5'10.
Cotto is thicker than Marquez but he has *****s in his armour that a fantastic counter puncher could exploit, hell it doesn't even take a fantastic counter puncher as we saw Zab, Torres and Pac give Cotto hell.
Khan would keep his distance and use his long arms to score on Marquez. Cotto would have to get in close and actually fight Marquez. Both guys have been in some wars but both still have some good fights left and imo this would be a FOTY canidate.