The pilot was practicing takeoffs and landings. He reported that he opened the canopy to vent the cockpit prior to takeoff; however, he was unsure if he verified that it was latched and locked. The pilot completed one takeoff and landing, and on the next takeoff, the canopy lifted off of the frame during the initial climb. The pilot unsuccessfully attempted to close the canopy and continued the climb, but was unsure if the airplane would maintain clearance from trees located beyond the departure end of the runway. He banked the airplane to avoid striking trees and the airplane entered a stall. The pilot pitched the airplane down, and was able to recover it from the stall; however, the airplane impacted the ground resulting in substantial damage to the wings and fuselage. A postaccident examination of the airplane and canopy revealed that there were no preimpact malfunctions or anomalies that would have precluded normal operation.