What is it
A canonical tag (aka "rel canonical") is a way of telling search engines that a specific URL represents the master copy of a page. Using the canonical tag prevents problems caused by identical or "duplicate" content appearing on multiple URLs. [source - moz.com]
Add content type tid 375 [bootstrap - insert code - head] to the section.
Add content type tid 375 [bootstrap - insert code - head] to the site config section of a particular site. This will apply the same rel-canonical tag across all pages in the site.