IF Canon were to get into a MF type situation, the company they should buy isn't Phase One or Hasselblad, it's Dalsa - the company behind the IQ1 and IQ2 sensors. If Canon can control the IP on the sensor technology it would give them a lot of firepower to go against Sony sensors.
This makes more sense, as it appears that most of the MF manufacturers source their sensors either from Dalsa or the former Kodak sensor division now Trusense Imaging. Trusense is owned by private equity investors - they would most likely be interested in turning a buck by selling out. Canon on the other hand could use control of more IP in the area of sensors - Canon would probably be more interested in getting access to and control of more sensor IP, especially technology that can be leveraged in Canon's core imaging business.
We would probably need to view a MF acquisition by Canon through the lens of what the acquisition would bring to Canon's core business.