The OP was never eligible for registration (which ended with the 1977 Act) or the special grant of citizenship from the 1977 Act (if that is what you are referring to). If the OP's grandmother became a US citizen as a minor when her parents became US citizens, she would have lost her British subject status and did not become a Canadian citizen with the commencement of the 1947 Act; I think this is the most likely scenario. However even if it is not, British nationality law at that time (as well as the 1947 Canadian Citizenship Act) did not allow married women to transmit their status to their children, or to allow birth abroad registration for said children. The 1977 Act was not retroactive to the applicant's date of birth, so even if the OP's parent was able to apply for it, the parent would only be a citizen from the day on. The OP would not be able to apply under the special grant because his/her parent was not a citizen until at least 1977, and the OP was born in 1962.