you may have misunderstanding - the GUI panel is not “inside” canvas. It’s a separate DOM element - just like webpage header, menu and content, the GUI panel exists separately from the canvas. You can do
gui.prototype.setDraggable(false)
to make it not draggable, but the mouse pointer still changes to the hand.
Disabling seems possible like this
gui.prototype.disableControl("shape")
and enableControl to make it active again. However it doesn’t grey out the interface, which is not great. But it’s a small open source project so that’s what you can get…