Windsor VIA rail to downtown Windsor/tunnel is roughly 2 miles. Taxis are available at station (station is manned most of the time). A little too far to walk. Tunnel Bus runs underneath and drops off at Mariners' Church/Renaissance Center.

Other than the to-ing and fro-ing, I think I'd just pick your friend up at the train station and either do Windsor or Detroit and be done with it (I think I'm reading that you'll have a car), or have him take a cab across (in the interests of time).