This is off topic and has been covered in a previous string. However, my limited understanding of the law is that if they show up at a border crossing and ask for asylum Canadian law says that since the US is a trusted partner, they by definition cannot be a refugee. However, if they make it across the border, then show up at any border services office, they will be considered for entry. So, there have been a significant number of previously legal American residents, who came under non immigrant type entries, for example Haitians, or Nicaraguans, etc, who are under threat of deportation who are heading north.
Ed