::::::I don't know what back-story you're referring to, Qex.
I'm sure you know what "let alone" signifies; it's a commonly used phrase. There's a full list of British, Scottish, and English monarchs on this page. As such, if there's going to be a link to a plain list of monarchs, why would it be to List of British monarchs? Its content and more is already here.
If the lines are the same back to 1707, why not then link to List of Canadian monarchs? It, at least, doesn't duplicate in its entirety the aforementioned list in this article.
Of course, there could be no link in the infobox to any plain list. It seems like a viable option to me. Ħ