I think this has been discussed before...but instead of digging, I can give you the gist...
Taking the US-Made machine back into the US should not be a problem. As long as machine going back into the US wasn't a re-import, the guy should have no issues. Bringing in the new machine, be prepared to pay the 13% HST tax (US made product=no duties). Since the machine coming back in trade has never been on Canadain soil, taxes SHOULD be collected even though no money is exchanging hands. You are going to need to put a value on the machine for the Border Officer, lest they will value it themselves and will probably use eBay...and we all know how skewed eBay prices are. I would suggest having printouts Pinside/PBRev/MAACA FS threads for the two machines in question, so that the officer can base the value for taxes from the documentation you provide.
I'm sure some will chime in with their own personal scenerios where taxes were not collected or they were collected at a lower rate. Also popular are those "What If..." scenerios looking for a loophole in the law to save a couple of bucks. That just muddies the waters. I've described the "What SHOULD Happen" scenereo above, your mileage may vary depending on how the officer interprets the situation. At most, you'll be on the hook for 13% of the pin's "market value".
