100 - 400mm IS L is a bit of an old lens with a first generation IS, at f/5.6 it's also very slow, new price is currently around £1200 The Sigma is less than half the price and again is a slow lens.
For wildlife and sport you ideall need as fast a lens as possible so here is a better alternative you might not have considered, the Sigma 120 - 300mm f/2.8 Incredibly shap lens capable of challenging the OEM's prime lenses (not quite as good though) and with the use of a teleconverter a 170 - 420mm f/4 or a 240 - 600mm f/5.6 This lens is the cheapest way to a 5 -600mm lens with working autofocus. up to 300mm it wll allow a massive 4 times as much light as the Canon 100 - 400mm allowing for much fast and accurate auto focus using the centre spot which the slower Canon cannot use.
Of course there's a bit of a problem, and that is the price - if you insist on new its £2k but second user you can get a good one for around £1K similar to the price of the Canon, but it's a much better lens!!
If you want to do the microadjuct on your lenses follow these instructions
here