To be honest (I say this as a vocalist) the best results you're going to get are by actually tracking multiple times. You can use things like Waves Doubler plug-in, a stereo delay, duplicating tracks and shifting them in time, etc. But nothing will have the visceral impact of simply recording the vocal numerous times.
If you recorded multiple times into the same Takes folder, you can always pull out one or another Take to use as a double, or make multiple Quick Swipe Comps and pull each out as their own track, etc.
I'd highly recommend doing that instead of using plug-ins to fake a multi-record/double.
The only true way to do it so it sounds doubled (nice or good) is to get the vocalist to sing it twice to different tracks. Don't waste your time with anything less. It all just sounds like a bad chorus
If the chorus's are similar (assuming you're doubling a chorus), I'll take the 2nd chorus and use that as the double on the first, and take the first chorus and use that as the dble on the 2nd. This has more to do with people not being able to sing a dble (a lot can't ). It helps to maybe turn the original way down, or off, and have them sing it again.
Here's an alternative to double tracking which is used to fatten up vocals: use a combination of panned delays and reverb to thicken your vocals. This can be achieved in logic pro with the use of buses - the multi-meter analyser is also used to check the width of your vocals. I have posted a video of this technique at: