I can understand Canon's (& Nikon's) concern about the new wave of cheaper, more DSLR-like medium format cameras heralded by the Pentax 645D. They pose a threat to the market position of the 1Ds (DXx) series of cameras by tempting those budget conscious professional users that need high resolution, but may not necessarily need all the speed and AF sophistication that the 'Canikons' offer. Because of this, I can see why there are rumours of Canon entering the MF market.
There are problems with both of the strategies they could use in order to do this. To go-it-alone would require Canon to develop technologies that are outside of their current experience. The alternative, the aquisition option, might seem attractive but it is fraught with its own difficulties. With the consolidation of the MF market in the last few years, (Pentax aside) there are really only two MF camera companies left: Phase One and Hasselblad. Both of these seem to be reasonably successful and therefore expensive to aquire.
I struggle to see what commercial advantage Canon could possibly gain by entering the MF camera market. Canon might be better served by concentrating its resources on gaining market share its current core market and accepting the loss of some of its high-end market.
Sorry for the long post!