Hello Mrs. D,
By 1979, when you applied for a passport and were told that you weren't a Canadian citizen, there had been many layers added to Canadian citizenship laws, and it certainly seems within the realm of possibility that an error was made. In particular, it is possible that some civil servant confused the requirements for people born abroad to Canadian parents before Jan. 1, 1947, and those born afterwards.
In all honesty, I must tell you that I am not an expert, and I may well be mistaken myself. So take what I say below with that in mind.
It would be quite helpful if you could say what the reasons you were given by the authorities at that time were. This is partly because I may be missing some point due to my lack of expertise, and partly because there are a multitude of ways people could lose their citizenship in those days. It would of course be easier to hear what they told you than to go through the list of reasons you might have lost it or might never had it. If you no longer have this information, you may be able to obtain it through a Privacy Act request to Passport Canada.
As far as I can tell, here are the laws applicable to your case, from the Canadian Citizenship Act, 1946, which entered into force on Jan. 1, 1947, as amended in 1953.
4(1) A person born before the first day of January, 1947, is a natural-born Canadian citizen, if
(a) he was born in Canada or on a Canadian ship and was not an alien on the first day of January, 1947;
or
(b) he was born outside of Canada elsewhere than on a Canadian ship and was not, on the first day of January 1947, an alien and either was a minor on that date or had, before that date, been lawfully admitted to Canada for permanent residence and his father, or in the case of a person born out of wedlock, his mother
(i) was born in Canada or on a Canadian ship and was not an alien at the time of that person's birth,
(ii) was, at the time of that person's birth, a British subject who had Canadian domicile,
(iii) was, at the time of that person's birth, a person who had been granted, or whose name was included in, a certificate of naturalization, or
(iv) was a British subject who had his place of domicile in Canada for at least twenty years immediately before the first day of January, 1947, and was not, on that date, under order o deportation.
(2) A person who is a Canadian citizen under paragraph (b) of subsection one and was a minor on the first day of January, 1947, ceases to be a Canadian citizen upon the date of the expiration of three years after the day on which he attains the age of twenty-one years or on the first day of January, 1954, whichever is the later date, unless he
(a) has his place of domicile in Canada at such date; or
(b) has, before such date and after attaining the age of twenty-one years, filed, in accordance with the regulations a declaration of retention of Canadian citizenship.
“Alien” here means, essentially, someone other than a a British subject on Jan. 1, 1947. People born in Canada were automatically British subjects at birth. It was possible to lose British subject status, but since you and your father's only connection was to Canada and Britain, this seems unlikely.
So as I understand it, you were a "natural-born Canadian citizen" from the moment Canada had its first fully-fledged citizenship act, i.e. 1947. (Before that you were a "British subject," as were most Canadians.) However, in order to keep your citizenship, you needed to either file a declaration of retention between the ages of 21 and 24, or have your "place of domicile" in Canada on your 24th birthday.
There may be some technicalities about how long you had to have been living in Canada, maybe five years, but I'm a bit confused about this. I haven't been able to locate a full copy of the 1946 Act on the internet.
There are other ways Canadian citizens could lose their citizenship under the 1946 Act, but these tended to apply to "non-natural-born citizens." As I've mentioned, you appear to be a natural-born citizen under the 1946 Act.
Nonetheless, there was a condition applying to minors who were never admitted legally to Canada:
6. Notwithstanding anything contained in section four or section five of this Act, a person who is, at the commencement of the Act, a minor born outside of Canada elsewhere than on a Canadian ship and who has not been lawfully admitted to Canada for permanent residence, or who is born after the commencement of this Act and outside of Canada elsewhere than on a Canadian ship, shall cease to be a Canadian citizen upon the expiration of one year after he attains the age of twenty-one years unless after attaining that age and before the expiration of the said year
(a) he asserts his Canadian citizenship by a declaration of retention thereof, registered in accordance with the regulations; and
(b)if he is a national or citizen of a country other than Canada under the law of which he can, at the time of asserting his Canadian citizenship, divest himself of the nationality or citizenship of that country by making a declaration of alienage or otherwise, he divests himself of such nationality or citizenship:
Provided that in any special case the Minister may extend the time during which any such person may assert his Canadian citizenship and divest himself of the other nationality or citizenship, in which case upon so doing within the said time he shall thereupon again become a Canadian citizen.
I don't know if this would apply to you. Since both your parents were Canadian, this seems unlikely. [Edit: It seems that your father was probably a "Canadian citizen" under the Immigration Act, 1910, as "a person born in Canada who has not become an alien." However, that didn't make you a citizen under that act, and therefore when you entered Canada in 1943, you may have had to be subject to some "landing" procedure. However, there would possibly have been an exemption for children of men in the military, so this may not be true. Perhaps this landing problem was a sticking point, if you didn't have landing papers when your mother brought you back to Canada, or they've been lost by the government. See http://www.canadiana.ca/citm/specifique/immigration_e.html for the legal texts.]
Another thing that comes to mind is that if you married a foreign husband at a certain time, you may have lost your citizenship.
I'm not entirely clear on what you wrote - did you ever apply for naturalization?
If I'm correct and you've actually always been a citizen, it would be worth speaking to a lawyer to have your citizenship recognized. One of the issues may be claiming OAS and other benefits retroactively - there may be limitations in this respect, and there may be advantages to filing claims as soon as you can for all these things. Sometimes the amount depends on the length of time you've been in Canada under some status.
Let me add what CIC Operational Manual CP 10 "Proof of Citizenship", Section 2.7, says:
2.7. Documents establishing citizenship
Claim to citizenship
Born outside Canada to a Canadian*
parent before January 1, 1947
* A British subject parent who would
have been considered a Canadian
citizen if the 1947 Act had come into
force immediately before the
person's birth.
Type of document
• Birth certificate showing parentage, issued by the
responsible government authorities in the country
where the person was born.
• Provincial or territorial birth certificate, or other
documentation to establish that the natural father, or
the natural mother if the parents were not married at
the time of the person's birth, was a British subject at
the time of the person's birth.
• If the person was not a minor (under 21) on January
1, 1947, proof of admission to Canada as a landed
immigrant (immigration document or British passport
used to originally enter Canada if it includes original
entry/admission stamp).
• If applicable, parents' marriage certificate.
Source: http://www.cic.gc.ca/english/resources/manuals/
http://www.cic.gc.ca/english/resources/manuals/cp/cp10-eng.pdf
It's not clear to me why no mention is made of proof of residence at age 24.
