He is a Russian citizen and would get a Canadian visa for this purpose (as well as a US visa, of course). He used to travel to the US on business and got harassed every time (late issuance of visa, always got into secondary screening during immigration etc.)

Is there any difference between an arrest and a detention at all, in the context of immigration? In both cases, you get locked up, and in both cases, you have no rights, because it happened during immigration and not during a crime investigation. Or am I wrong here?

So does the US CBP have detention facilities in Canada, or are detained persons being forcibly transferred to the States?