Using 7d with 100-400l looking to upgrade glass for nature and sports?

The 500/4 is a great lens, but it is very heavy for hand held work, though it isn't impossible. I have no idea how you would shoot from a kayak with such a rig. A 7D + 500/4 will weigh over 10 pounds and will be about 18 inches long.

You might spend some time analyzing the unsharp photos to see if technique could fix it. Why are they not sharp? Is the lens not sharp, was the focus wrong, shutter speed too slow, IS ineffective?

I have 7D, 100-400 and 300/f2.8. The pictures I got using 300/f2.8 are sharper than 100-400, but not of huge difference.
I suggest you put the 100-400 on tripod, use live view 10X to focus manually, and shoot a non-moving target. If you are not satisfy with the sharpness, then it is your 100-400 that causes problem.

I had so much fun and such a high success rate shooting with my 7D and 100-400mm on my Bald Eagle trip in the Skagit Valley, from a raft.
But I can totally imagine how it is even harder from a kayak!
I didnt get the shot I wanted but I blame that totally on me. The Servo on the 7D works so great and the combination with the 100-400 is perfect. I'd practise a bit harder and, ideally, try another sample of the same lens (a friend?) to see if it's your lens or yourself. Good luck!

Whenever I hear someone say a particular lens doesn't produce good results, it usually means one of three things.
1) The lens is bad (poor optical quality)
2) The lens is out of tolerance and needs adjustment
3) User error

My 7D w/100-400L combo produces extremely sharp images. If you're not getting that, then take a look at 2 and 3.

Sorry for the double post. Here's a tight crop from the above image.

Wow, I'm all thumbs this morning. My apologies again. One more time.

Please post an example with the EXIF intact, if possible. There have been too many threads about 7D issues that turned out to be user errors. My combo of 7D and 100-400 produces perfectly sharp images. What shutter speed were you using, was the IS on, what AF mode did you use, how were your custom functions configured, what IS mode did you use (1 or 2) etc. etc.

I was beating myself to death wondering what happened to my lenses or my technique when I bought a 5Dm2. But when I set the proper microadjustment to each lens it brought the WOW factor back. I believe the 7D has MA capabilities also. Worth a try. Good luck.