If Canon intends to keep things secret until 2 March, surely their reps would have neither the freedom nor, possibly, the information to confirm anything to dealers before the due date. If I were a Canon rep continually being asked about the 5D3, I would think the best way of calling off the hounds would be to (mis)inform dealers that the 5D3 won't be announced on 2 March, regardless of the truth.
One thing that bugs me about the recent 5D3 pictures, though: would they still have pre-production 5D3s in the field so close to an announcement?
On balance, my money is still on CR being right.