Yeah, this seems pretty clear:
"This means that in most cases you’re automatically a Canadian citizen if you were born
before December 15, 2025
outside Canada to a Canadian parent
This rule also applies to you if you were born to someone who became Canadian because of these rule changes."
The act also specifies:
"A person who would not become a citizen under one of the paragraphs of subsection (1) for the sole reason that their parent or both their parent and their parent’s parent died before the coming into force of An Act to amend the Citizenship Act (2025) is a citizen under that paragraph if that parent — or both that parent and that parent’s parent — but for their death, would have been a citizen as a result of the coming into force of that Act."
If I'm reading that right, it still applies if your parent and grandparent are dead but your great-grandparent was a Canadian citizen.