The Canon is a nicely built lens, its pretty similar to my 100mm f2.8 L IS Macro. The macro lens is known as a lightweight 'L' lens due to the plastic barrel..it might not be in the same league as other Pro Lenses build-wise.
I opted for it for the overall package, image quality, glare/flare control and distortion handling were the primary reasons based on what I read.
The aperture is middle of the road, not the fastest, not the slowest. It has the best range (10-22) of the top contenders.
I think its the lightest lens from the list, some may see that as a negative re build quality, but presumably a lighter lens for landscapes is a positive considering the typical gear taken, tripod & head, fliters etc.
I believe the Canon DPP software recognises the lens and can auto correct issues within the application - I've not got any other lenses other than Canon so can't confirm truth if this is the case.
There is no pouch/case or hood, again you might end up using square filters for landscapes removing the hood requirement. I don't use any cases/pouches as the lens goes in a bag with some more kit and the body.
It has a closer minimum focus distance and FTM USM compared to the Tokina - these two facts possibly swung it for me over the Tokina. The Sigma was equal with the Canon here, but lost out in other areas.
The other tiny little fact/niggle for me is I prefer my lenses to zoom/wide on the same rotational direction of the barrel. I think Canon is the oddity here, most other lenses zoom clockwise whereas Canon is anti-clockwise - very small issue lol.:bonk: