Is the Canon EF 24-105mm f/4L IS USM Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 70mm f/16.0 test image. Observe the contrast and resolution of these results.
Is the Canon EF 24-105mm f/4L IS USM Lens set to 70mm f/16.0 sharper than the Nikon 24-120mm f/4G AF-S VR Nikkor Lens set to 70mm f/4.5? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.