If you paid for the item in US dollars, you'll pay the taxes in US dollars.
If you paid for it in Canadian dollars, you should/will pay taxes in Canadian dollars.
Otherwise you'll be paying 10 or 12% more or less(whatever the exchange rate is). Much easier to charge you in the same unit of money than convert it half way through.
So...only if you paid in Canadian and got taxes in US will you have been screwed over.
Try the math.
$100 US *1.12(tax) = $112 US = $123.20 Canadian (at 110% exchange rate)
$100 US = $110 Can. $110 *1.12 tax = $123.20 Can.
Its the same thing.
Putting shipping in there wouldn't change anything, it'd still work out the same.
And if it lists everythign in US $, it's safe to assume you'll pay shipping and taxes in US. They're not going to switch half way through the transaction.
PS: I havent read every post, so i might just be spewing out what MEM has said already.
[This message has been edited by Stubby79 (edited 04-12-2014).]