Yes, it will... I frequently use mine with a 100-400mm attached.![]()
Again a yes - I have a 60d with a sigma 135-400m that fits fairly easily.
I believe it is called a 400 as aimed to fit a camera + 400mm lens?
(500 = camera + 500mm lens)
I carried a 40D with 400mm f/5.6 attached in my Flipside 400