Hi Mary

The S. Wallace on the CWGC site is the one you are looking for. I had a look on www dot collections canada dot gc dot ca and if you look for the WW1 records do a search for Sydney Wallace. They have free images on there for him. The regimental number is the same on this site as on the CWGC site for S. Wallace so it is him. I had a quick look at the images and it mentions the Isle of Man.

Regards,

Col