Sanchez is one of my all-time favorite fighters. However, much as I hate to pick against him, I don't see him beating Whitaker. The one style Sanchez would have had trouble with is Whitaker's.
Sanchez could throw enough punches and, if the fight takes place in any one of a few certain places, the judges may award him a very close split decision.
However, in all fairness, Whitaker would be too difficult to hit cleanly with more than one punch at a time. The one loss Pernell has at lightweight was a robbery against Jose Luiz Ramirez. It's possible for Sanchez to win a close decision but the likely outcome would be
Whitaker by unanimous decision.