The better/most effective way to use Melodyne in SONAR XNx is to use Regions. Select the region or clip (if it's not too long) and then go to Region FX drop down menu at the top left of the Track Pane. There you can select Melodyne and the clip will automatically open in Melodyne.
BTW, you might find help in the SONAR X series forum just above this one.
Kind regards,
Living Room Rocker
P.S. You may have to update SONAR X3 to X3e. Rewire was not compatible with x64 until rather recently.