It can be done is the short answer. However it will take time and skill and would probably give far better results by getting a better in tune recording. The studio guys I work with have a saying that it is better quicker and cheaper doing a good retake than trying to edit a bad first one.
FYI I prefer using Melodyne than autotune. It is worth noting that Cubase 5 has a good Melodyne type plugin already built in.