Mouse Listener For Two JPanels

The program i am creating consists of two JPanels (currently) and one canvas. The canvas is in the center of the JFrame, while flanked by JPanels where both have 13 buttons each.

To paint a simple picture, my program will draw letters on the middle canvas when a button is clicked.

I created my own buttons that implement the ActionListener interface , so when a button is clicked it will display its character in the console. But my question is, How do you implement the listener to draw something on the Canvas when the button's are clicked?