Tirerack is a really good deal if you intend on buying wheels at the same time from them as they will include road force balancing and mounting for free which is about a $150-200 value. I always get roadforce balancing because I find that it is identical to the balancing quality of factory mounted tires and wheels. Standard balancing often has slight vibrations at highway speeds. Importing tires from across the border yourself also has the advantage of possibly not paying any tax which in BC is a 12% savings right there. If you make a weekend trip of it, it could even be a guaranteed tax free purchase depending on the price and the number people travelling with you.
I guess pricing in Ontario is more competitive than BC. My winter tires for example are Dunlop Wintersport 3D and they are priced at 1010tires for $290 for each front tire and $330 for each rear tire. I got it for USD$212 and USD$242 respectively from Tirerack. Shipping was $69.
Total from 1010tires = $1240 before shipping
Total from Tirerack = USD$976 (CAD$1005) including shipping to WA
I ended up picking it up in two separate shipments and I only paid taxes on the fronts which amounted to $50 so my grand total post taxes was CAD$1055.
If I had bought locally, after HST it would have been $1389 assuming there is no shipping cost.
This has been my experience buying tires anyways especially with winter tires. I suppose a local dealer might be able to match prices but I've never tried. The differential seems quite high. I remember Costco asking for $245 a tire for Michelin X-ice tires for my Mazda 5 which I got from Tirerack for only $118 each.