You didn't mention if you will be using a full frame or 1.6X crop factor camera. I use full frame, and for the type of work I do (seascapes mostly), the 17~40mm f4 L lens is the lens I seem to use most, mostly at the wider end. I also have a 24~70mm f2.8 L, that I use as a "walkaround" lens, but often when a great seascape with big sky presents itself, the 24MM isn't wide enough. I know you mentioned primes, but the above two Canon zooms, I find, hold sharpness in 20"x30" prints, and I am not sure Canon's shorter primes would be any sharper.
Good luck
Dave