They're still making 5D2 and selling at around $2400. If this "new high end" is announced at $2500, it will instantly kill the sales of 5D2 that they still have to clear the stock of.
If they are still making 5DII and expect to continue selling it after this new end camera is announced, it would suggest the following:
More expensive than the 5DII - If it would be at a similar price, it would instantly kill sales of the 5D as you say....no matter whether it is named 5D3 or not.
Not named 5DII or 5DX Canon will reveal a 5D3 at some point - but they will not be selling it alongside the 5DII - in fact, just announcing a 5D3 will kill sales of the 5DII, simply because it will create the impression that the 5DII is "obsolete".
So, again, IF they are still making 5DII and plan to do so for a while, it would actually make sense to have a February announcement of a $4000 "3D" (or whatever - just not a 5D3), and then a $3000 5D3 late in the year.
True, there is still that price point of around $2000 for a entry FF camera that sell like hotcakes
Nikon kept the D90 alive well after the D7000 and D5100 came out and it still sold well
so if they continue to sell there would be no reason for canon to stop making 5Dmk2s over all
the value for money of these cameras is very good