What happens if you have two different canonical URLs listed on the same page, you know where they point to different URLs. John Mueller from Google said on Twitter that leads to the canonical information being undefined. So Google will use other signals to determine the canonical URL, if needed.
Ryan Mews asked the question and said in his tests, he thinks that Google just ignores the canonical information. John said, yep - it is undefined. John added "also, rel-canonical isn't a directive, it's just one of the signals that flows into the canonicalization process."
Here are those tweets:
AFAIK it's just undefined (so if you want it to do something, write it right). Also, rel-canonical isn't a directive, it's just one of the signals that flows into the canonicalization process.
— 🍌 John 🍌 (@JohnMu) November 5, 2020
Have you all seen the same outcome on your end?
Forum discussion at Twitter.