Hi LasPalmas,
I see you answered your own question. To quote from "Over the Front" by Franks & Bailey, "Though often listed as a French-Canadian,
Emile Lussier was in fact born in Chicago, Illinois on 10 Oct 1895. He remained there for the first 15 years of his life and was educated there, but then went to Canada in 1910 when his father took employment building RR stations from Winnipeg to the Pacific coast. When war came, Lussier was living in Alberta and joined up, giving Medicine Hat as his home address. Enlisted in the RFC," etc. etc.
"After the war he returned to the USA where he found... that the American authorities considered him an American citizen by birth, despite his parentage. He remained in the US where he became a farmer. In WW II, as the US remained neutral, he joined the RCAF, serving with No. 1 Wireless school and later commanded Nos 1 and 4 Wireless Schools, becoming a Squadron leader." After the war he returned to his American farm and lived his last years in Westminster, Maryland, where he died in 1974.
So I guess he was one of many folks of that era who had a sort-of dual citizenship, in some ways.
Greg