Was wondering if I can do a square 255/35/20 set up without any issue in terms of rear fitment or if I absolutely need the staggered 255/285 setup. Seems easier to find winter tires for the square 255 setup all around... thanks!

There's a thread on this topic already. It is fine to be square. In some ways it will be safer.

I'm running staggered 2010 SC and go all 19" no stagger for snows.

FYI, I ordered from Detroit Wheel and Tire. Worked out well here to Ontario. I see you are as well.