Officine Creative definitely isn't worth their high retail prices but you can often find them on sale (Barneys had that same boot in a light grey for ~50% during their last sale off I believe - though it seems to be back at full price now [=http://www.barneys.com/Officine-Creative-Distressed-Derby-Boot/501567287,default,pd.html?cgid=men&index=1][/
Quality on the pair of OC's I had was good, although other people on the forum have had problems; solid mid-tier brand if you get 'em on discount.
DXB, for Toronto snow you are going to need some serious sealant like Sno-seal. And then there's the zipper (if the model you're looking at has one) which isnt sealed.. depending on how deep your slush is water could get in there. Personally I wouldn't think of risking a $1k pair of boots in heavy slush. Salt is the real killer though.. once you get a salt stain on leather it's not coming out.
Then there's the question of warmth.. Guidi's are a fairly thin boot (was it sinndk who called them "leather socks"?). You'd probably need to size up an extra 1 or 2 sizes to be able to wear a thick wool sock underneath. Ohya, and you'd need to get a rubber sole with some serious grip added. A layer of vibram isn't gonna cut it in the snow.
You may want to look at other options.. N.D.C. makes some shearling-lined winter boots with a commando sole. Not exactly Guidi styling though.. if you're after that but snow-ready it might be hard to find. You might wanna message Uncontrol.. forum member with like 10k posts who lives in Montreal - I remember him going through a lot of options a while back on the (non-baller) shoe/boot thread.