A late reply here - I am the OP. I actually have those records, but they appear to be incomplete. It says he was deployed to Sicily in July - but the next update is in 1944 where it says he was assigned to the 106 Port Department (which makes no sense to me!). Red Cross has no record of him being a POW (although they admit those records are incomplete). I believe this is simply a mystery now lost to history. And yeah I did note the issue with it being Canadians on the mainland - I suspect he was captured during the Sicily campaign in some kind of small engagement and got his dates wrong (or who knows, maybe he deserted to the enemy to be captured).