With the strength of the CDN$ don't be afraid to order from USDealers. As mentioned above, 999 Ag/Au is GST/HST exempt.
Mind you, the CBSA postal customs people often don't realize the tax exemption and force collection of HST on delivery but if you get nailed with a charge when your package arrives you can claim the money back by following the process on the import receipt on the package. It takes between 1 and 2 months to get cheques back from the CBSA though...but they will come eventually.
If you have the sender clearly mark the package with the correct import code, it significantly increases your chances of being properly assessed as exempt coming in through customs.
Have the sender put (for discretion, you might want to leave out the "silver" word):
".999 Ag/Silver Bullion" import code/tariff #: 7118.90.00.99 ***GST/HST exempt
In my notes I have written 7108.20.00.00 for gold and 7118.90.00.99 for silver, but you might want to double check -- there are some pdfs with tariff/duty/import codes somewhere on the government site, but I don't have a reference link.
Info on disputing a improper assement and getting a refund if you were charged HST can be found at:
http://www.cbsa-asfc.gc.ca/import/postal-postale/dispute-contestation-eng.html
As a funny note, last winter an order I got from the Perth Mint was marked and declared as "Metal Samples" ...needless to say, it didn't get the exemption and I had to go through the adjustment/refund process. Overall I bat about 50/50 on getting nailed. Ebay/personal looking packages usually come through ok -- packages from a "business" and clearly marked with value, etc on the customs forms are what generally ahve the tax charge applied (incorrectly).