run 14s, they're cheaper than 15s.. trust me on this, 15s will be lower profile and therefore lots of $$$$
If you run 14s the cheapest size to run without throwing your speedometer off would be 175/65-14s, you want to run the skinniest tire you can find for your car (OEM tire size is 185/60-14) as skinny tires will cut through snow like nothing.
I ran 185/65-14s last year on my corolla and had no problems.. this only because I got a better deal buying that size as they seemed to have an overstock on them.
BTW, you sure you need snow tires? I thought BC winters were mostly rain.