Why wait until March and not CP+?? At this point, a month shouldn't make a difference.
A month means greater ROI on the existing model.
Or possibly this; (cut from Wikipedia)
"The Canon EOS 5D Mark III is a professional full-frame digital single-lens reflex (DSLR) camera made by Canon. It has a 22.3 megapixel CMOS image sensor. Succeeding the EOS 5D Mark II, it was announced on 2 March 2012, the 25th anniversary of the announcement of the first camera in the EOS line, the EOS 650. It was also Canon's 75th anniversary."
What better way to mark the 28th and 78th anniversary than by releasing another new body with a sensor that out specs the competition.
Yeah, anniversaries are nice and all...but shareholders prefer ¥.
These days, they might even prefer $.