The Calgary Highlanders pipers definitely wore Royal Stuart tartan kilts and plaids in early years , You are correct.
The crossbelt furniture and belt are not strictly Gordon Highlanders pattern, I saw photos of same belts have been wearing of some other pipers, and even many civil pipers wore it.
The only obscure and still open question for me in this photo is a sporran, similar to the one worn by pipers of 2nd Batt Gordons.
but maybe there is a same answer - it's typical pipers sporran and it has a cantle without any regimental features...