IMO rim size doesn't really matter, it's the fact that aftermarket wheels are usually a lot wider, thus, when in slippery conditions, the weight of the car is spread out over more area, leading to reduced traction. Wide tires in the sun is all good, not so much in rain ice and snow.
Get snow tires or the 19 s and you should be OK.
...oh wait, you're in Canada, you're screwed
