Neither the current VIA Windsor station or Amtrak Detroit station are easily accessible for a tunnel route. Amtrak has talked about putting a new stop for cross-border service at the old Michigan Central Station, which is currently being redeveloped by Ford. Not sure what VIA would want to do; I imagine they'd want to avoid moving since the trackage between Chatham and their current Windsor station is one of the few segments they own outright.

As discussed in the article, the other big barrier to Toronto - Chicago - Detroit service besides the stations will be the delay at the border, partly for customs inspection and partly to deal with freight congestion in the tunnel.