I have found that many items I want to purchase online have free shipping in the lower 48 states. To take advantage of this I use a service called
Kinek which will accept shipments for as low as $5.
They have warehouse locations at many US border cities. For example I use Buffalo NY, but user there is one in Ogdensburg NY, near Ottawa. When I am crossing back in to Canada I declare all purchases and pay taxes as required. Always cheaper than shipping in to Canada. I usually fill up with gas and pick up a few groceries while in USA to.
A lot less hassle than trying to go to UPS warehouse and using the self declaration method.