miji.beURL canonicalization is a technique that consolidates multiple URL variations existing for the same content into one representative URL, gathering the search engine's evaluation in one place. There are cases where technically different URLs point to the same page, such as with or without www, with or without a trailing slash, a different order of query parameters, or HTTP versus HTTPS. If these are left as they are, search engines may judge the content to be duplicate and its evaluation may be split.
There are three representative means of canonicalization. The first is declaring the canonical URL with a rel="canonical" tag, the second is permanently forwarding from non-canonical URLs to the canonical URL with a 301 redirect, and the third is registering only canonical URLs in the sitemap. In parameter canonicalization, the URL with tracking parameters (utm_source, etc.) removed is treated as canonical, and URLs with parameters reference it with a canonical tag.
The relationship between short URLs and canonicalization is important. A short URL itself is not a canonical URL and functions only as the source of a redirect. Google's documentation explains that permanent redirects are used as a signal that the redirect target is the canonical URL, and in the case of a permanent redirect, the short URL itself is not expected to appear in search results.
As a practical point, if a URL shortener uses 302 (temporary) redirects, according to Google's documentation, temporary redirects are not used as a signal that the redirect target is the canonical URL. If you prioritize SEO, the safe course is to check in advance which redirect the service you use returns. Also, issuing multiple short URLs for the same page splits your access analytics, so it is advisable to follow the principle of one short URL per page.