I read that Adorama started processing for shipment during the night.
Amazon processes shipments around the clock.
Is it possible that B&H and Amazon had the largest orders so Canon simply loaded their trucks last? If Canon shipped in order of smallest orders to largest, that would explain why all the mom and pops got them first, then Adorama, B&H, and Amazon.
The reality is Canon can only ship them out so fast, so they have to decide whether they want to cast a large net first and get them in the hands of a bunch of retailers right away, or, fulfill the largest retailers first and make everyone else wait.