Hello DJ Fish 1, a very warm welcome to the thread. I can only reiterate smudge's comments that anything relating to your Great Uncle's record will be of great interest and perhaps some more light may be shone on it here.
You have already uncovered a wealth of detail from his service, and the sequence of units before his operational squadrons are many and interesting. I would suggest (though Danny will be the arbiter) that 31PY might refer to Moncton, which was 31 PD (Personnel Depot) through which it seems all RAF aircrew trainees in Canada passed before and after training. In 1945 it became RCAF No 1 Y Depot. It might be that the Y prefix preceded the RCAF takeover. There is talk here of a Y Depot at Moncton in 1943:-
No.31 Personnel Depot, Moncton - and it's successors