Here is a direct response from George over at the Tesla site forums.
gblankenship | August 15, 2012Hi everyone. There seems to be a bit of confusion surrounding this issue.
Brian H, you are correct.
pbrulott, unfortunately, all cars manufactured in North America cannot be imported into Canada duty free. In order to be duty free, a minimum percentage of the car must be made in North America. Model S falls slightly below that percentage, so our cars cannot be brought into Canada duty free. We must pay the 6.1% import duty. We do not have a choice. That is the only reason why we are including it in our pricing.
I hope this helps make things a little clearer regarding the 6.1%.
Regarding the overall math, here's how we see the build up:
US Base price
+ $1,500 USD for interior upgrade
+ 6.1% duty
+ 1.5% to 2% for incremental transportation and business costs
Then convert this total using a mid-term currency conversion rate
That's the way we did it.