North American T-6 Texan (N15797)

The FAA lists this bird as a HARVARD MK IV, built by CANADIAN CAR & FOUNDRY, which matches what you listed, Max. So, if you use the ICAO code: T6 (the code for a North American AT-6 Texan), that is probably as good as you'll get for this bird. I can't explain the PA28 code.

How about this? Simply go with what the FAA designates this aircraft, N15797, to be as Greg states... which is a Canadian Car & Foundry Harvard Mk.IV built in 1945...

https://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?NNumbertxt=15797

And that makes T6 the appropriate entry in the box for Aircraft Type under Photo Tags.

Love the canopy open for a little ventilation!