As long as you declare what you have in your car when you come back to Canada, there is no problem with Canada customs. Going into the States, you just tell the officer you are picking up goods that you had shipped to Hagen's and that's no problem either.
Canada customs charges whatever the applicable duties & taxes would be on your purchases. However, from my personal experience, they rarely charge duties due to our free trade agreement with the USA. So, you typically pay pst+gst on most purchases.
