I've found Adorama to be very reliable. Some have had issues with B&H because they get so many orders. I learned to avoid Amazon. If you order immediately, B&H or Adorama are fine. I've never ordered a new introduction direct from Canon. If you have a local dealer, check with them. They will likely get you one faster. Dealers may have them a day or 2 early in some cases so they can start deliveries on the official first day.
With delivery services overloaded, a lower priority product like a camera may take longer, and warehouses may need to take longer to pick and pack.