From Americans at War in Foreign Forces: By 1916, the Toronto exhibition grounds had become the point of conversion for Americans into members of the Canadian Expeditionary Force, though the actual numbers of who they were could never be precisely known. Figures from Canada’s Department of Soldiers’ Civil Re-Establishment in 1927 can be considered official, though ambiguous: “Enlistments into Canadian Units through the British Canadian Recruiting Stations at various points in the United States: 31,000. Enlistments through the same medium into British Units: 13,000. The official figure of men who on enlistment in the C.E.F. gave their birth places as United States or Alaska is: 35,612.”
Though this was the most official document about American enlistments in the C.E.F. that can be found in Canadian records, the true numbers would be variously reported and speculated upon during the war, and impossible to know definitively in any examination. In many cases, determination of whether the individual was an American citizen by birth or naturalization, or simply an American-related individual through immigration or family connection, or an American presenting himself as Canadian has to be carefully made. Please see Americans at War in Foreign Forces for a full discussion of the variables and ambiguities involved, especially at a time of economically driven and fluid movement back and forth across the American-Canadian border.