Not even close. Manny is a superior hitter. His OBP is always around .400, and slugging pushing .600.
Bay is a top OF, but not at the same level.
Manny for Bay...no way. Bay plus alot more would be needed.
IMHO.

I did trade Manny and Scott Ruffcorn (remember him?) for Barry Bonds. That was several years ago. It's only this year that Manny outperformed Bonds. Manny is about as close to Bonds as there is in MLB.