I think it depends on why the 2 channels are unbalanced in the first place.
It could be either: (i) the mics had different level settings, or are not well matched; or (ii) your recording position/mic placement was such that the stereo image is unbalanced.
If its the first, then do what has already been suggested and amplify one channel. If it's the latter, try a stereo image plug in (eg Waves S1, or something similar) that allows you to rotate an asymmetric stereo image. You might get better results, i.e. less noise, better image, this way.