Unfortunately, duty has been a pain since the good ol 1800's!
I used to ship computer equipment from Canada to the US - the paperwork for each item (mouse, keyboard - you get the picture) was about 30 pages per shipment.
Clothing is has one of the largest % duties along with shoes - around 20/22 %
example - Shoes- $20
now add duty - 22% - $4.40 = 24.40 USD
24.40 x exchange rate of 1.59 = 38.78
http://money.cnn.com/markets/currencies/americas.html
add any excise taxes and the like = 38.78 +5
43.78 x GST (fed tax) 7% = 46.84
(Prov tax should not be charged - this can only be charged by a company who has a provincial sales tax number - i.e. UPS in Toronto charges a processing fee, then PST can be charged on the processing fee)
If you are going for a road trip with your chapter, most US campus tend to have a Greek store where letters/t-shirts can be made. Call about 2 weeks before and order one, and then pick it up on yur visit. If you are out of Canada for at least 48 hours, you have up to $200 Cdn of goods you can bring back duty free.
For more info, visit Canada Customs and Revenue Agency at
http://www.ccra-adrc.gc.ca/menu-e.html