How to use two Canvases in Unity 4.7 ?

I have two Canvases with different UI elements (buttons). And I can press only buttons from first Canvas, if I try to press buttons from second Canvas - nothing happens, but if I disable the GraphicRaycaster of first Canvas, then I can press the buttons from the second Canvas. How make it able to press all buttons from both canvases? (not at the same time, of course)