Warranty will work in Canada. The rule is that whatever warranty benefits you'd normally receive in the US you are also eligible to receive in Canada (which I believe are exactly the same, making this rule irrelevant for now). This applies to portable devices ie. iPads, iPhones, etc.
You can order an iPad from the US store with a Canadian credit card but you need a US shipping address, and I don't think they offer shipping to store (?)
When the Canadian store didn't have any, in October, I bought an iPad Mini from the US store and had it shipped to a US border town 20 minutes from my house.