What's the huge deal with the 200-400? It is a nice range to have ... and Canon has 400mm covered in 4-5 lenses at different price points does it not?
It has a built-in 1.4x extender which makes it a 280-560mm f/5.6 lens as well.
That's 900mm on a 1.6x body, with AF.
1D IV, 5D III, 5D II, 16-35L II, 24-70L II, 24-105L, 70-200L IS II, 300L IS, Σ 50, Σ 85, 1.4x III, 580EX II, 600EX-RT