I am pretty sure this site does not have this tag. Why though? ELL has this tag, in which a person can post a canonical post intended as a reference for questioners.
That's a meta tag. According to the blog post on meta tags:
The reason meta-tags are a problem is that they do not describe the content of the question. They describe some other aspect of the question, like the author’s skill level, or the author’s motivation for asking it, or generally what “kind” of question it is (poll, how-to, etc.).
I don't think the tag should exist on EL&U or ELL. At best it's simply not useful. (When I'm looking for an answer to an English question, it doesn't matter how the question was made.) At worst it's being used instead of a tag that would be useful, one that describes what the question is about. (Note the ELL question that only has the [canonical-post] tag.)
Instead of using meta-tags, I find the canonical by either looking at the highest voted questions in a tag (example: highest voted tense questions) or by finding one of the many duplicates via search (example: questions linked to our tense canonical). You can also see the most linked-to questions by using the frequent tab.
And one more important thing: "canonicals" aren't always questions that were asked by meta consensus or even by someone who knew the answer. A lot of questions become canonicals because of the effort put in by the answerers to create a thorough explanation. (And this may be the final reason why I find the tag on ELL not useful: Where are all the "organic" questions that serve as canonicals? Who gets to determine what counts as one of those?)
Here I am in the process of finding a question to be a canonical on a specific topic, since I saw a mess of open, duplicate questions: "Why don't we close these duplicates?" vs "Why do we not close these duplicates?" vs "Why do not we close these questions as duplicates?".