Free shipping only from Amazon Canada. $45 USD shipping is ridiculous. Tap Magic is $15 CAD for 16 oz from KBC Canada and I can pick it up. $4.89 for the little 4 oz can.
But often the shipping charges from Amazon US are less than the difference for the oddball things that are not available. I am waiting on some electrical cord cover for my office floor to get power to the credenza. Amazon Canada has some for same day or next day shipping but they're made from something like PVC and come rolled up (and like to stay in that shape, according to reviews). The ones I want are silicone and don't take as much of a set. I think shipping was $10 US or something like that, no big deal. Liquids are more of a hassle, especially if they attract hazmat charges.
More interestingly you can buy a lot of things from Amazon.de and Amazon.jp (you have to set up a separate account for each) though the shipping charges can easily double the price, there are some cool things that are just not easily available otherwise.
It's a great time to have a bit of disposable income, between all the cool stuff available from China, Japan, Europe and US sources (not to mention surplus from local North American sources) we have an embarassment of riches.