The Hreflang Tag
Hreflang tags tell Google which version of a page to serve based on the searcher's language and region. It prevents your Canadian site from competing with your US site.
Subdomains vs Subdirectories
For international SEO, subdirectories (e.g., website.com/ca/ and website.com/uk/) are almost always better than subdomains or ccTLDs because they consolidate domain authority.