If you're living in Canada or Mexico -- but close enough to the border to make a trip to a US Apple Store -- Clean My Screen has posted instructions for reserving an iPad outside of the US. There are 23 steps in the guide, but it doesn't look terribly complicated.
It involves the creation of a new account with a US address and no payment method, but with a real email address. Then you can confirm your account and make a reservation, although you'll need to make a trek (or have a friend in a convenient location do it) to a brick-and-mortar US Apple Store to retrieve your iPad.
As noted in the article, having a US iTunes account can be handy for a handful of other reasons, including being used to buy free apps and music, and potentially get free eBooks once the iBook Store opens. If you live outside of iPad reservation territory, give it a shot and let us know how you fare.