I have not used multitouch before in JOGL so I can't help you that much (unless you point us to an existing multitouch example).
But I am a bit curious why it could make sense to have multitouch on GLCanvas. I presume multitouch can only work on mobile phone or tablets, hence on Android only (?). Since Android does not support AWT, you can not use a GLCanvas in Android as GLCanvas inherits the AWT Component. Am I wrong?