Originally Posted by
After Burner
Those who cross the US border frequently and accumulate a significant day count are well advised to check the following website frequently. This is the data CBP looks at. Mistakes can be made whereby an exit (US to Canada) has failed to be recorded which will result in an erroneously high US day count. If this has happened, it's good to know in advance.
https://i94.cbp.dhs.gov/I94/request.html
Canadians aren't issued I-94s though, so the search would come back empty. I tried searching for myself and it couldn't find me.