Guzman would be a great opponent for Pac, but so would alot of other fighters.
Unfortunetly for Guzman, Barerra and Marquez are the big money fights for Pac. Guzman just isnt a draw at this point.

Personally, I'd like to see Guzman and Valero go at on freeview HBO.
The winner of that fight would get the exposure they need, and get fans clamouring for a matchup with Pacquaio.