After you trace your circles, just use a sponge brush and acrylic paints to fill them in! I planned out where I wanted each color and just wrote in each circle with pencil (lightly). You will probably want to do 2-3 coats. Make sure you paint the wrapped sides of the canvas if any of your circles go off the edges - it looks funny if you leave it white.
I purchased some wall hangers at the home improvement store for about $2.50 in a pack of 3, and nailed them to the backs of the canvases. (Measure the canvas and mark where the center is, then line up your wall hanger. I used a push pin to poke a little hole where each nail should go, that way when I used the hammer I didn't slip and put the nail in the wrong place.)