Hi! I have the Canon 17-40 f4L and I simply love it! it's really sharp (at least my copy ) and is perfect for landscape, where I usually shot with at tripod at f16 or so!
I used it a few years ago during a trip to Grand Canyon with a Canon 350D and now I use it on a Canon 1D mkIII.
I heard really good things about the 35mm f1.4 Sigma, but I fear that for landscape (and even more for the WIDE landscape of Grand Canyon) it's way too limiting. On your camera it's equivalent to a 56mm, so a standard lens, and instead you would probably need a wide angle.
By the way, in Grand Canyon I went down South Kaibab Trail at dawn... I totally recommend you to do it, even if you have to wake up at a weird time... there you can take amazing photos as soon as the sun rise through the canyon.
Don't forget your tripod and enjoy your trip!