Canonical and hreflang solve different problems
Canonical signals the preferred representative URL for duplicate or near-duplicate content. hreflang helps search engines select language/region alternatives. One should not be used as a substitute for the other.
Use real locale alternatives
Every hreflang row should point to an actual equivalent page for that audience. Do not generate country variants that do not exist.
Reciprocity matters
Large international implementations should ensure equivalent pages reference one another consistently. This local builder validates the table you enter but cannot crawl remote pages.
Use x-default only when it has a real purpose
x-default can identify a language selector or fallback page. It is not mandatory for every international site.