The Canon is a great lens, but according to TDP, the Zeiss is slightly sharper from f/1.4 to about 2.8, where the Canon catches up to the Zeiss in sharpness. I got the 35L because I wanted AF and use it mostly taking pictures of family, especially kids that are almost always on the move.
If you are looking to make a decision soon and are willing to work with a MF lens, then the Ziess is the way to go. But of course, everything could change when/if Canon comes out with the 35L II.