A brief explanation happens in Search engine optimization (SEO).
In general the system will generate the canonical using the same logic as for cHash.
Excluding arguments from the generation¶
TYPO3 will fallback to building a URL of current page and appending query strings. It is possible to exclude specific arguments from being appended. This is achieved by adding those arguments to a PHP variable:
$GLOBALS['TYPO3_CONF_VARS']['FE']['additionalCanonicalizedUrlParameters'] = 'example_argument_name';
It is possible to exclude nested arguments:
$GLOBALS['TYPO3_CONF_VARS']['FE']['additionalCanonicalizedUrlParameters'] = 'example_argument_name[second_level]';
Arguments in general should be excluded from cHash as well as
See the possible options in Caching, regarding excluding arguments from cHash.
The idea behind that is:
If a URL is worth caching (because it has different content) it is worth having a canonical as well.