From Wiki:
The 128th Battalion, CEF was a unit in the Canadian Expeditionary Force during the First World War. Based in Moose Jaw, Saskatchewan, the unit began recruiting in late 1915 in that city and the surrounding district. After sailing to England in August 1916, the battalion was absorbed into the 15th and 19th Reserve Battalions on August 24, 1916. The 128th Battalion, CEF had one Officer Commanding: Lieut-Col. F. Pawlett.
My wife’s Grandfather was in the British army in WWI. He must have traded pins with a Canadian soldier. That’s the only way I could see it ending up with my wife’s Aunt.