Using tagging for this - particularly mod-only tags - feels like bureaucracy for its own sake. 

A sufficiently good "canonical" question should naturally migrate to the top of the Votes/FAQ lists in its respective tags. When repeatedly used as a target for duplicate questions, it'll start showing up in the list on the "Close as Duplicate" dialog. If you need a separate list of these, a post linking to them (which you already have) should suffice. 

**And all of this is either directly accessible to everyone, or automatic *based on* stuff that's accessible to everyone.**

Forcing mods to mediate every single "canon or not canon" discussion just adds resistance to a process that already has plenty of that simply by its nature. They should be able to weigh in like anyone else, putting on that diamond hat only when a dispute *requires* mediation.