I spend time in both countries, and I've discovered a few things that I'm better off buying in Canada. Do you know of other things to add to this list?
Netflix: I subscribe to Netflix Canada basic @ 7.99 CAD. But I almost exclusively use it from the US. Versus the US price of 7.99 USD, this is a 24% savings for the exact same service!
Contact lenses: I found that my brand is cheaper in Canada (I'm buying them from clearly.ca). Even with the shipping, they're cheaper than what I can get in the US (e.g. Walgreens in store or on-line). This was a surprise to me, but once you convert currencies it's cheaper in Canada.
Domain names: I have several, and I've migrated nearly all of them to 10dollar.ca. Every time the US renewals came up, I noticed they were getting more expensive (largely due to FX rate).
Other things? I also find fruits & vegetables are much cheaper in Canada but you can't haul those over the border.