This option is set to “on” by default and will check each page to see if there is a rel=canonical tag on the page and confirming it points to the same page. You can uncheck this option and we will not check for canonical mismatches. This can result in a significant number of errors in your XML site maps.
If you use this feature and it finds a mismatch it will show an error report code of CAN or 301 CAN.