Well, whatever you do your tires are going to stick past the flares. You could add 1" spacers to your Canyon's and then adjust the steering stops and keep the tire mostly under the stock flares. That would give you 4.5" BS. I wouldn't go with less then 4.25" if you want to stay under the stock flares. 8" wide wheel with 3.75" is going to put around 4" of the tire outside the stock flare. You'll need 6-7" wide flares to cover the tires 100%.