Crossing border question..

I seen a pinned video earlier of a trucker going right through Mex/US border without being questioned much... and with all this talk of open border down then why is that the CAN/US border is so damn strict for Canadians coming down? Why is it if you have so much as a speeding ticket they know about it and will harrass you for coming over. And if you have any record you cant come in. Why only Canada getting the tenth degree???