Yeah you could use CanvasToLayer. If your canvas size is 640x480 and you want to spawn an object in the middle at 320,240 then you need to convert that canvas position to a layer position. So the position on layer 0 would be:
CanvasToLayerX(0, 320, 240), CanvasToLayerY(0, 320, 240)
or in general:
CanvasToLayerX(0, WindowWidth/2, WindowHeight/2),
CanvasToLayerY(0, WindowWidth/2, WindowHeight/2)