Is the Canon EF 17-40mm f/4L USM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 17mm f/4.5 test image. Observe the contrast and resolution of these results.
Is the Canon EF 17-40mm f/4L USM Lens set to 17mm f/4.5 sharper than the Rokinon (Samyang) 14mm f/2.8 IF ED UMC Lens (Orig) set to 14mm f/2.8? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.