Canonical tags are HTML link elements that signal to search engines which URL should be treated as the authoritative version of a page when duplicate or near-duplicate content exists. The tag goes in the HTML head: <link rel='canonical' href='https://yoursite.ca/master-url/'>. Google uses canonical tags as a strong (but not absolute) signal of which version to index and consolidate ranking equity into. The scenarios where canonical tags are essential: (1) ecommerce sites where filter or sort parameters create dozens of URL variants of the same product list — canonicalize all variants to the clean parameter-free URL; (2) ecommerce product pages reachable through multiple categories — canonicalize to the primary category path; (3) syndicated content that you've republished from another source — canonicalize to the original publication URL; (4) AMP versions where the canonical tag points from AMP to non-AMP and vice versa; (5) paginated archive pages where you want the first page treated as primary; (6) URLs reachable via tracking parameters (UTM tags, fbclid) — canonicalize to the parameter-free version. Every page on your site should include a self-referencing canonical tag pointing to itself. This is the safest default — it explicitly tells Google what you consider the canonical version even when no duplication exists, preventing accidental canonicalization to an unintended URL via Google's automatic detection. Canonical tag mistakes to avoid: pointing canonicals at URLs that 301-redirect (Google ignores the canonical and may pick its own); pointing canonicals at non-existent URLs (404s); pointing canonicals at URLs blocked by robots.txt; canonicalizing too aggressively across pages that aren't actually duplicates (you'll suppress unique content from indexing); and using canonical tags as a substitute for proper redirects when you've actually moved content (use 301s instead). Canonical tags are signals, not directives. Google considers your canonical declaration alongside other signals (internal links, sitemap inclusion, hreflang, content similarity) and may choose to ignore your canonical if the other signals strongly contradict it. For Canadian bilingual sites, canonical tags must be coordinated with hreflang — each language version is its own canonical, with hreflang declaring the language relationships.