Pilot reported strap or harness caused loss of canopy resulted in return to departure airport.

Narrative

While flying aerobatics over the ZZZ airport in an aerobatic practice area (APA). The canopy of my [aircraft] departed without warning. Other than being very windy without a canopy; there was no change in the handling characteristics of the aircraft. I discontinued the aerobatic sequence; announced that I was landing and landed without difficulty on the active runway XX.The specific situation occurred 14:30 minutes into the flight during aerobatic practice. The specific maneuver was a half snap on the vertical downline at 120 knots. A procedure that I had performed on many occasions in the past; in this aircraft. The one change for this flight; was my seat positioning in the aircraft. I had placed myself further forward in the cockpit to better handle negative G's and for better control of the stick.I can only guess that a strap on the parachute or the seat harness caught the latching mechanism and pulled it open. The aircraft suffered only slight cosmetic scratches from the departing canopy on the tail and the right wing. The broken canopy was recovered in the field in the center of the airport/APA. I received no injuries.