I agree with ikas and Shaun. I don't think Prince of Wales's Leinster Regiment works here, because it is referring to his compnay, which wouldn't have taken the title Leinster. In an Infantry battalion it is more likely to be A, B or C Company etc. The 1st Tunnelling Company was an independent unit.
Going back to the service records at the LAC, there is only one Sapper mentioned, namely Sapper William John Weller 164213 who enlisted at Niagra on 7 Sept 1915. He was a plumber by trade and single. His mother was Kate Weller of 166 Sheridan Street, Brantford. If he is the man in the OP's document, there is no sign in his service record that he was ever posted to the 1st Tunnelling Company, and never went to France. Of the 104 pages comprising his record, most are taken up with medical and pay related matters.
