I often use ZTX for what you're trying to do. It is bundled in a large number of applications including TwistedWave, Digital Performer and ProTools. Unfortunately, you cannot just buy it standalone from Zynaptiq except as Pitchmap and that's pretty expensive.
Zynaptiq Changing instrument tracks in Melodyne more than a 3rd is a lot of work — no way do I try that with vocal tracks. Just sounds weird.
For voice only, the AVOX plugins from Antares (Autotune) might be the best. They're available individually or as a suite. 30 day trial.
AVOX 4