I find that when the Gm Global Connect website gets an update that the vehicle has left BG on the transport, it has actually arrived at the Windsor border. It could be b/c The transporter scans the cargo upon arrival at Windsor.
For my C7 orders once I have the VIN I send an email to the transporter in a couple of days and am able to get a more accurate status and estimated delivery date. I don't know if it pushes them to rush the transport or not but since I've been doing this the vehicles haven't been spending 4-5 days at Windsor. Now they move within 1-2 business days. SmackYYZ's vehicle was at Windsor for way too long so I decided to take matters in my own hands for future C7's.