I mentioned this in the existing Ontario HSR thread but I think the topic is deserving of its own (correct me if I'm wrong). Given that, from what I've read here, US border formalities on the Amtrak Cascades are performed at the station in Vancouver and will apparently be done in Montreal soon for the Amtrak Adirondack, why not extend VIA into Detroit using the same scheme, but with the formalities taking place on the US side (inside the station in Detroit) rather than the Canadian side? Detroit is a metro area of, according to Wikipedia 2010 numbers, just shy of 4.3 million people. Makes all the sense to anchor the Toronto-London-Windsor service with another major metropolitan area.