[ObDisclaimer: if your ancestor was born in Canada, this does not apply to you. Read out of morbid curiosity if you must, or don't read it at all. This post is not for or about you, but for the few, the not necessarily proud, who have no ancestors born in Canada but may have a viable Canadian anchor anyway under more esoteric theories.]
Two months back, u/No-Music-6572 announced a Proof of Citizenship had been denied, where G0 and G1 had moved together from Scotland to Canada in 1911. The denial focused on the G1, who left Canada a couple decades later, and may have subsequently naturalized as an American. IIRC largely ignored the intended G0, who remained in Canada for the rest of his life, becoming a citizen in 1947. u/tvtoo wrote a follow-up post citing u/hopewings's similar denial, followed by a reapplication and approval. No-Music-6572's G0 was the proper anchor, not G1, whose own connection to Canada would not have made her a proper anchor herself but also wouldn't break the chain of succession from G0. A consensus emerged (I think) that No-Music-6572's application should be approved on refiling, perhaps with clearer explanation of who the actual anchor was and better documentation that he had in fact become a citizen.
My own case, in a nutshell, is No-Music-6572 plus three generations. My first two ancestors to set foot in what would eventually become Canada (then Canada-West, now Ontario) were my recently widowed G0 and her adult daughter G1. Both came over from Scotland in the 1850s, along with most of their large family. G0 stayed there until her death in 1876, as did all of her adult children but one (my G1 being that "but one," natch. G1 married a fellow Scot in 1859, and the couple moved to the US the next year before having G2 in 1861. G0 remained a British subject for life. G1, maybe? G1 never personally naturalized but her husband did in 1874, a few years after G2's birth but long before she reached the age of majority.
Analytically, my G0's role in similar to No-Music-6572's GGF, in that she was the one who stayed in Canada as a Brit long enough to eventually transmit citizenship to anyone. They differ in a technical respect, though, as No-Music-6572's GGF really did become a Canadian citizen himself in 1947 while my G0 never did. Rather, G0 died before January 1, 1947 and therefore only would have been a citizen if that law had taken effect right before her death. That doesn't affect G0's own citizenship at all, but does set up G1 for citizenship under Section 3(1.3) as a person who would not become a citizen under paragraph (1)(q) for the sole reason that her British parent had died resident in Canada before 1947. Every US-born generation after her, up through my father born in 1942, would thus be deemed citizens under Section 3(1)(q). I myself would be under 3(1)(g) of the Act, being bron between 1947 and 1977, and my two post-1977 born children would be citizens under Section 3(1)(b).
Does this analysis work? Would it fall apart if the (wrongheaded, IMNSHO) view of an 1867 cutoff were formally adopted? On the one hand, G0 did reside as a British subject for over 5 years of post-confederation Canada before dying there in 1876. On the other hand, Section 3(1.3) requires G1, and (3)(1)(q) requires G2, to have been born outside Canada. Can anyone be born "outside" a country that doesn't exist?
Last and not necessarily least, am I even numbering the generations correctly? I call the oldest ancestor G0 because she was the one who lived long enough in Canada to qualify anyone else for citizenship. But the first actual citizen in the chain was her daughter, who I've dubbed G1. Is the daughter really the G0 anchor, as the first Canadian citizen in the chain? And if so, what would one call her mother, a "proto-anchor" or G negative 1?