I think the details matter here. How long did he overstay his visa by? Was there other issues with his travels through the US? Did he have any legitimate reason not to renew his visa? If this was a matter of days, with no other problems with his visit, it first should have been seen if Canada would take him. The idea of incarcerating someone, at taxpayer expense, over a trivial infraction discovered as they left the country is a huge waste of taxpayer dollars.