I don't know why only the default printer appears. I use Easy Photoprint from CS5 all the time. In fact, it always comes up by default with my Canon Pixma Pro 9500 II, and it's not the default printer on my system. And for what it's worth, neither the default printer (Canon i9900) nor the Pixma Pro are physically connected to the machine. I have both on printer servers on my home network.
Cameras: 1DX, 1D4, 20D, 10D, S90, G2
Lenses: Canon 10-22mm, 16-35mm f2.8L II, 24-70mm f2.8L, 70-200mm f2.8L IS, 300mm f2.8L IS, 200mm f2L IS, 50mm f1.4, 50mm f1.2L, 85mm f1.2L, 1.4x TC, 2x TC, 500D macro, Zeiss 21mm
Lighting: 580EX, Elinchrom 600 RX's, D-Lite 4's, ABR800, 74" Eli Octa, 100cm/70cm DOs, Photoflex Medium Octa and reflectors, PW's, Lastolite Hilite, Newton Di400CR bracket