I would suggest leaving the original audio track in place, turn OFF snap to grid in SONAR (the "N" key toggles snap) and then manually move the MP3 around until it matches the original audio
You should be able to use both your eyes (as you may be able to see the audio transients in the original audio) but most importantly use your ears to confirm the audio is lined up - and then the ultimate test is both ears & eyes to check the dancing looks in sync
Good luck and it should be pretty straight forward