Guide / indexation
Canonical tags clarify a page’s preferred address.
Tracking parameters, print views and product filters can create several URLs for similar content. A canonical link is a hint that helps consolidate those signals.
Point to a real, indexable page
The canonical should resolve, return a successful status, and contain substantially the same content. Use an absolute HTTPS URL and keep the choice consistent in internal links, sitemap entries and redirects.
Canonical is not a redirect
Visitors remain on the requested URL. If two URLs should never coexist, a redirect is clearer. Do not canonicalize unrelated pages merely to funnel authority; that creates confusing signals and poor user journeys.
Audit the common variants
Compare protocol, host, trailing slash, case, parameters and pagination. Test the chosen URL and inspect generated HTML. Keep one canonical tag per document.
Good rule: the canonical page should be the page you would link to if you had only one URL available.