Aircraft Landed with Gear Up

C-GPZN, a privately registered Lake LA-4-200 aircraft, was conducting circuits during a local flight from Saskatoon/John G. Diefenbaker Intl, SK (CYXE). During the approach to Runway 27 for a touch-and-go, the landing gear selector lever was not selected down and the aircraft landed with the landing gear retracted. The aircraft sustained damage to approximately 42 inches of the fuselage keel strip.