My diagnosis is twofold: the 17-40 is not Canon's sharpest lens at 17mm. It's far from horrible, but when you compare it to shots from a 135/2L there is a definite difference. Try stopping down to 11 and/or look into the 16-35/2.8L. That said, the file can still be made into something quite nice:
A full-sized 3.1MB JPEG can be downloaded here
I used a combination of ACR, Neat Image, Focus Magic, and my Midtone Sharpening Actions
to process the image. I know there's sensor dust, but didn't bother to clone it out, as that wasn't the issue being raised.