Multiple citizenship (dual) not legal until 1977.
By the 1930s and the outbreak of World War II, Canada’s naturalization laws consisted of a hodgepodge of confusing acts,[3] which still retained the term “British subject” as the designation for “Canadian nationals”. This eventually conflicted with the nationalism that arose following the First and Second World Wars, and the accompanying desire to have the Dominion of Canada’s sovereign status reflected in distinct national symbols (such as flags, anthem, seal, etc.).[4] This, plus the muddled nature of existing nationality law, prompted the enactment of the “Canadian Citizenship Act, 1946”, which took effect on 1 January 1947. On that date, “Canadian citizenship” was conferred on most Canadians previously classified as “British subjects”. Subsequently, on 1 April 1949, Canadian nationality law was extended to Newfoundland, upon the former British colony joining the Canadian confederation as the Province of Newfoundland.
Canadian nationality law was substantially revised again on 15 February 1977, when the new “Citizenship Act” came into force. From that date, multiple citizenship became legal. However, those who had lost Canadian citizenship before that date did not automatically have it restored until 17 April 2009, when Bill C-37 became law.[5] The 2009 act, the most recent major change to laws governing Canadian citizenship, limited the issuance of citizenship to children born outside Canada to Canadian ancestors (jus sanguinis) to one generation abroad.[6]
Birth in Canada[edit]
In general, everyone born in Canada from 1947 or later acquires Canadian citizenship at birth. In one 2008 case, a girl born to a Ugandan mother aboard a Northwest Airlines flight from Amsterdam to Boston was deemed a Canadian citizen for customs purposes because she was born over Canada’s airspace.[7]
The only exceptions concern children born to diplomats, where additional requirements apply.
https://en.wikipedia.org/wiki/Canadian_nationality_law
Thanks - good info. The issue is the interpretation that Canadian law would nullify US law for a child born of a US parent in Canada. US law states that the child is a US citizen, as long as (per law in effect at that time) the US parent had at least 10 years physical presence in the US prior to the birth, including at least 5 years after age 14. I read the 1947 Canadian law as not allowing Canadian citizens to deliberately acquire a second citizenship. The intent was not to deny US citizenship at birth to a child born to US parents if that birth happened to occur in Canada.
I do agree though that there are some fuzzy edges here ...