The conventional wisdom is that when stopped down to f/8 or so, there's not much difference between the IQ of the 17-40 and the 16-35 II, the latter costing twice as much.
Neither lens is particularly good for architecture - both have significant distortion at the wider end.
Instead, you might consider the TS-E 24mm II or the TS-E 17mm - both are excellent for architecture and landscape, the movements allow you to compensate for keystoning (keeps the vertical lines of buildings straight) and allow very deep DoF without stopping down so far that diffraction costs you sharpness.
