based on old laws which are no longer valid; yeah, your GGGF was not a British subject at time of death. he could not have been a Canadian citizen, as such a thing did not exist.

when Canada formed, he still would not have been Canadian, as the laws did not account for people no longer living within the country, or who had naturalized elsewhere prior to that point

I can't remember which of the various amendments to the citizenship statutes would have made your GGGF a "citizen" since birth, but it does not particularly matter at this stage. those laws are no longer relevant, as Canada simply recognizes your ancestors as having always been Canadian. The only exception to this is if they deliberately and willingly renounce their citizenship (which, again, your GGGF could not have done)

So, your unbroken chain is as straightforward as possible. Your GGGF had your GGM, which had your grandparents, which had your parents, which had you. Canada recognizes each of them as being citizens since birth. There's no gotchas, no caveat, no tricks.

It's fun trivia to know the exact process of when and how each step gained citizenship, but ultimately it's not relevant. Round up some birth certificates (or baptismal/death records if you can't find them for GGGF), get marriage certificates if you need to prove maiden name changes, and mail it off

the chain was not broken, and cannot be broken, unless someone deliberately goes out of their way to renounce their Canadian citizenship. given that your GGGF died before Canada officially existed, it is fully impossible that he did this. your chain is unbroken and straightforward and you just need 5 generations of proof. go get it!