If it costs $25 to ship to US, then it's $25 to the US. Simple as that.
Then you pay the fee for using their office, and depending on the weight of the thing you bought, then it'll probably vary from as low as $3.50 to ______.
Now when you head back to Canada and you declare $450, you will most likely get sent in to get checked up, which you will then pay.. 12%? I think...
Either way, you save money when you ship to the states.
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Just last week, I got charged for buying 2 front lips for US $500. I guess I got sent in because the boxes were just so damn huge. In the end, I paid like $62 in taxes? Probably would've been better for me to ship to Canada on my end.. But in your situation, it's still pretty good
Good Luck!