It's been a while since I've bought track in quantity so I can't help you there. You probably won't find any real deals on track and much other stuff here in Canada. We're just too small a market for discounting hobby supplies.
If you want a box of track - 25 pieces - its probably the best to order from a discount shop in the US. We don't have to deal with customs, just have to pay the standard GST/HST that you would in your home province. The usual big cost is shipping to Canada. Some places with great prices such as Trainworld in Brooklyn charge a flat US$25.00 shipping fee; others are lower or higher. Usually only worthwhile if you're making a big order, I've combined with friends to share the shipping costs.
And if you should go this way, make sure they don't ship to you using UPS or one of the delivery services such as FedEx; they charge outrageous fees to collect the GST/HST (US$25-35!). Have stuff shipped by US Mail, our Canadian Post Office will charge you $5.00 to collect the GST/HST. Often there is no tax on smaller parcels.
Good luck!