According to his attestation papers, dated August 12, 1915, Winnipeg,
His next of kin is Mrs. F. Stewart, (his Grandmother) Gladstone, Manitoba, Canada.
He was 18yrs 11mos.
Clarence was b. August 22, 1897, Carberry, Manitoba.
1916 census - Manitoba
Clarence Galloway (ethnicity, Scotch) was living with his Grandmother Flora Stewart and his widowed Aunt, Kate Stewart.
The 1906 census also shows Clarence, aged 10yrs, living with his Grandmother, Flora.
My guess is that he was an orphan being raised by his Grandmother.
This could be a tough one finding living family. Good luck.