Surface is cheaper than air. Check the tax. If you're purchasing from outside your province or state, there should be no tax. If you're purchasing within your province or state you'll pay the applicable sales tax. If you're going for a short trip to the US you could ship your stuff to your destination, and bring the stuff back over with you and claim it with your overseas purchases, duty free.
Returns are difficult at best.
You may have to pay shipping twice, which would be a real pain. And then you would need to reclaim your GST from the government. Check that the company has an excellent reputation and return policy first. Use the Internet to research the companies you want to purchase from.