[boxstershorts]

A couple of clarifications:
-The letter you need from Porsche N-america is to say that it has no outstanding recalls on it (not to say that you can import it)
-Porsche North America is one of the rare companies that actually recognises warranties when crossed into canada but call them with the VIN to confirm the warranty exists to begin with.
-The 72 hr american customs delay: It depends on what border you cross. Some borders don't allow the car across (it has to stay there for 72 hrs) while others even allow you to fax the title to them 72 hrs ahead of crossing the border which completely eliminates the delay. I recommend calling whatever border you plan on crossing before doing the deal.
-If you get a US transit permit you have to pay US tax (and then try to get reimbursed later...not easy I'm told).
-The duty is 6.1%, GST is 6% on top of that. And then you have PST.
-The federal inspeciton is done (free) at canadian tire and takes 10 minutes if the mods are done.
-In Quebec the provincial inspection costs 75$ and is much more in depth (measure exhaust, braking force at each wheel etc)
-Not all US Boxsters are offered at a better price than you can find in Canada. Be patient.
-If you pay 25KUS, your final out of pocket is around 33KCAN incl all fees and taxes except shipping if you truck it up to Canada.
-Ask all questions about every step (purchase details, payment in US funds, warranty, shipping, border crossing, inspections) before you make any offers. And get a CARFAX, dealership inspection at the very least.
Hope this helps!