I'd go with the Tamron 17-50 or canon 17-40. The Tamron should be sharper and is f2.8. The Canon should have better color and contrast (Less interesting in the days of digital.) and way better build.
If you can stretch your budget get the Canon 17-55f2.8 IS. It really is canon's best crop lens.
Good luck finding a razor sharp Tamron 17-50 F2.8 when wide open. It is exceedingly easier to find a Canon 17-40 F4 razor sharp wide open. Of course for landscape this matters little, so for the better color rendition and contrast, I'd opt for the Canon 17-40L.
I don't know what the OP's budget is, but I've had great results with the Canon 24L and especially the 35L. The 50L is great at F8 through F11, and all three provide great color and contrast.