Braxus
I do not use Canon, but would like to help you. I have Nikon and Zeiss F2/100 mm Macro. My logic is, if they made that all fits and works the same as original Nikon lens for Nikon cameras, no concern they will make it the same way and for Canon. Zeiss have exceptionally good engineers that really knows what they are doing.
Mechanical quality is better than original Nikon lens: turning the barrel, resistance to turning, no play, diaphargm works fine, no oil on diaphragm, I use a lot and still no any play in turning the barel, finish is nice, I live in Toronto - cold weather as you know already but turning the barel is the same as on summar time, filter thread is fine (you will have orther option for filter), lens shade comes with a lens,...
And for optical quolity of ZF lenses. You will find no better lens. My F2/100 ZF is nothing behind F2.8/100 APO-Macro Elmarit by Leica which is one the best lens Leica ever made, and might be the best optically and mechanically too that is ever made for any format.
Your 50 mm lens is not that good optically as 100 macro, but that is for all 50 mm lenses for 35 mm cameras. Bokeh is what it lacks, the same as, again, for any other similar lens. However I would expect as it is a real German, Zeiss, the best 50 you can buy. If you get, i guess, the same optical quality lens for Leica and you will pay $4000 CDN. Knowing Japanese lenses, I think you will be glad to invest into you business or joy that money for Zeiss lens.
Also I would take care whre you buy it. If you get in Henry's or Vistec no wonder to find a fingerprint on its lens (my experiece). The best place to buy is B&H-NYC. They never open the lens box and it is as packed by manufacturer. It is they policy. Again take care whre you buy it now not later.
Daniel OB
www.Leica-R.com