Step One: determine whether the recorded track is truly stereo. An examination of the waveform is usually all that is necessary, but not always.
Should there be no obvious visible differences between the top and bottom waveforms, it can also be determined by summing left and right and looking at the difference. This isn't as hard as it sounds. Any M/S plugin that lets you adjust Mid and Side levels independently will do. I recommend the free Voxengo MSED plugin over Channel Tools for this.
Listen to the track while turning the Side knob up and down. If it's a dual-mono track, meaning the left and right sides were somehow combined during recording, then there will be no change in tone or volume as you move the Side knob. A true stereo track, OTOH, will noticeably change.