To me a good canonical question has the following attributes:
- Addresses a commonly encountered question.
- The question itself is fairly clear.
- The answer is sufficiently concise to be readable, but detailed enough to be a complete answer.
- The answer is widely accepted to be the best answer for the question.
- Can be used as a Duplicate-Of target for close-votes
That last point is why so very few of our canonical questions are on meta.
That particular question, regarding *AMP installers, is primarily about category topicality which isn't a good fit for the canonical tag. If it's anything, it'd be a better fit for faq; the question is in a similar vein to this one about professionals.