All these Dope Engineers..lol Excited, my B. But everyone has already spoke on it. Waves has a Stereo Imager that can widen them to a degree. But stacking usually does the trick. Sometimes Ill do 3-5 takes of the exact same style, then Ill tell the artist to do it again but in a diff way. That way I have multiple styles to choose from & stacks so I can Comp them together; what I need.
Reverb, as Dave Pensado says makes things "front the back" and panning "left to right." Which I thought was a great analogy. what type of track is it? Is this a Hook you want "wider?" Stacking, harmonies, dubs, ad libs, all of that thickens the audio. Then you can pick & choose what you want to use.
Slight delays, reverbs, pitch shifting by a few cents. Idk what style of music your trying to use this method for but most hip-hop/rap vocals are tight & in your face with low if any type of ad libs. Take a listen to the radio or pick up an album & take a listen for yourself. Hope this helps. Peace