canonical-link is an appropriate tag for its use.
Canonicalization (c14n) is specific computer science term that should stay its own tag. I've added a tag-wiki (could be done better) to it.
Robert is right that the tag-wiki entry for canonical shows it to be a meta-tag. I imagine someone is using that to try and label canonical answers, like this latest question talks about. Since there is no process for that yet, it going to be arbitrary, but maybe the Team needs to make a decision on how to handle "canonical" answers before we get rid of it.
EDIT: I've gone through canonical and most of the ones I fixed were about the URL tag (or pages), so I've retagged them canonical-link. There have been a few that shouldn't have had the tag for any reason, and a few that should have had canonicalization. I've flagged for a moderator to create the synonym, and they have. I'll also go through the canonicalization questions and convert those that should be to canonical-link.