Forget used unless you know how old the tires are. It`s your first Cdn Winter so be properly prepared.
If you are buying new, go down to 18″. You get a taller tire and less expense. Also go narrower to cut thru the snow better.
Mantis Racing in Oakville can do an 18″ Pkg for around $3000. Mount/Balance/Installed consisting of Pirelli Winter SottoZero`s 235/40/18 Front and 265/40/18 Rear mounted on 5 Star Rims w/TPMS.