In the USA the titles show any leins against the car. A lein realise form is only needed if there is a outstanding amount owed on the car (otherwise the title will show no leins on it) and you would have to get it (the realise form) from whom the money is owed to. IE the PO's bank, credit union, ect.
Down there (As far as I know) if you borrow money and use the car as collaterial the person lending the money usually holds the title in their possession. So if the person dosen't have the title in their possession when you go to pay for the car, don't give them any cash.
And as to your question about the border crossing, US Customs searches for any leins when you produce the title for them to stamp before exporting the car to Canada. IF the title shows a lein, then that is when they will ask for the realise form.