if you need to do pitch, formant and amplitude correction, celemony melodyne is great for it. it does analysis and then offers you multiple ways to correct pitch, etc. it also comes in several different versions with different feature sets
if you're going to use pitch correction, i'd tune the instruments with a tuner and then correct the singer to the instruments. pitch correction doesn't work on polyphonic sources (more than one note at a time as with a guitar chord).