It is a background check. USA uses your fingerprints for air travel authentication. Canada uses an iris scan for authentication. The authentications are separate but the travel history is shared for visa tracking purposes. It is much less invasive than being queried and documented on varied subject by every singe border agent. The files on you grow much bigger with the unlimited scope of questioning of a border agent. Of course, they can still stop you and ask you details (and do) but I have found once you are on file they stop digging around into your private life because they know you have a background check on file.