When 5(2)(b) was implemented with the 1977 Act, it was done as naturalization because unlike citizenship by descent, it was not retroactive to the applicant's date of birth. Prior to 1977, married Canadian mothers or unmarried Canadian fathers could not pass down citizenship to their children; 5(2)(b) was introduced in the 1977 Act to correct that oversight. When the 2009 Act came about, those that had acquired citizenship through 5(2)(b) had it converted to be by descent under 3(1)(h), so now they would be deemed citizens since birth instead of the date they were naturalized.
If you would like to follow up on my research, click here:
https://www.canada.ca/en/immigratio...citizenship/acquisition-loss/acquisition.html
If you were to go to the note under 3(1)(c), it states:
"Persons who were born outside Canada between January 1, 1947, and February 14, 1977, to a Canadian mother (in wedlock) or to a Canadian father (out of wedlock) and who were granted citizenship under paragraph 5(2)(b) of the 1977 Act are described under paragraph 3(1)(h) as a result of the 2009 legislative amendments."
Then if you were to follow that to 3(1)(h), it states:
"
Paragraph 3(1)(h) recognizes as Canadian citizens persons born outside Canada to a Canadian parent between January 1, 1947, and February 14, 1977, and who did not become citizens by descent, but who were granted citizenship under section 5 of the 1977 Act before April 17, 2009. Under this paragraph, such persons are recognized as citizens by descent as a result of the legislative amendments on April 17, 2009, instead of citizens by way of grant [pursuant to subsection 3(6)], and their citizenship is retroactive to their date of birth [pursuant to paragraph 3(7)(
e)]."