I'm not sure I believe the third-party sellers who say it is in stock. There's no way Canon would give them stock before Amazon or B&H gets it. More likely, they take your money now and ship it next week when everybody has gotten their allotments.
Some of the 3rd party sellers on Amazon indicate 'in stock, takes 2-3 days to ship' meaning they may not have it but have been told to expect a shipment. B&H indicate that it's expected on Friday. But some retailers do get it ahead of others...for the USA, consider - they are crated and shipped over the Pacific Ocean, so they arrive on the west coast first, so west coast retailers get them while another part of the shipment is on a truck heading for B&H and Adorama on the east coast.