get the f/4-5.6 version instead of the faster f/3.5 model.
Cheap, light, small and very good IQ.
The other thing I've been lead to believe with the Canon 10-22 .. at 10mm you may get vignetting if you don't use a thin ring CPL.
High quality ultra slim CPLs cost a lot more money than the std versions of the same quality CPL glass.
With the Siggy 10-20(4-5.6 version!) a std CPL will not vignette at 10mm.
While many people may frown upon using a CPL at an UWA focal length of 10mm .. there really is nothing wrong with doing so in a lot of situations.
What
CAN happen with using a CPL at such short focal lengths is that it may render unevenly blue skies when the sun is at a particular angle relative to the lens.(you see this a a darker blue patch in a plain blue sky).
The other alternative to consider is not spending any money on a new lens at all, and instead using your current lens(which has a good reputation) and learning to do panorama/stitching.
So maybe the money otherwise spent on a lens(Sigma 10-20 can be had for ~$400) could be spent on other stuff such as a good tripod(if you don't already have one) or some accessories for doing panorama/stitching.