If it needs to be a zoomlens, you could look at the Sigma 100-300 f/4 or the Sigma 120-300 f/2.8 OS. You could also look for the Canon 300mm f/4L IS.
Honestly, I think it would be a waste of money, in what situations, do you need these lenses where your 70-200 and 400mm wouldn't suffice?
You could sell them both and get the Sigma 120-300 f/2.8 OS with 1.4 converter to replace them.
Canon EOS 70D / Canon Eos 450D / Sigma 10-20mm f/4-5.6 / Sigma 120-300mm f/2.8 OS / Canon 50mm f/1.8 II - Canon 18-55mm IS / Kenko Pro 300 1.4 DG / Sigma 2x APO DG / Canon 430 EX II Flickr
/ 500px
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