As covered here, a canonical page is the preferred version of a set of pages with highly similar content.
When you use a canonical link, you're essentially letting Google know that you have highly similar or identical pages, but of them, the canonical page is the preferred one to index:
Adding this link and attribute lets site owners identify sets of
identical content and suggest to Google: "Of all these pages with
identical content, this page is the most useful. Please prioritize it
in search results."
Ideally, you would only add this to pages containing the same content. If however you add them to a non-relevant page unintentionally, Google should understand that these pages are not related and (hopefully) index them individually.
In these kinds of unknown situations however, which are dependent on variations in content, it's always best to preform A/B testing if possible. In any case, you only run the risk of a page not being indexed, which you can verify within Google Webmaster Tools.