I have heard via a rep that Nikon plan to release a camera in the Autumn and then one in the Fall. He also claims that he knows Canon are releasing two models in the interim periods. Which are of a similar level and quality. The first from Nikon in the D700 replacement and then next is a D3 replacement.
Nikon has already scheduled a press conferance on August 24, and the details and availability of the new models have leaked. http://nikonrumors.com/2011/08/02/august-24th-nikon-d700-and-d3s-successors.aspx/
However, Canon has yet to schedule any press conferences. You do not introduce a new pro camera model without a big press splash, so we are all waiting to hear of a upcoming press anouncement.