I just imported two rifles from the USA to Canada. While it is legal to do so, many of the companies will not ship a PAL-rated airgun to Canada(I couldn't find any). I live in Thunder Bay, which is about 45km from the Canada-USA border. I ship the rifle to my USA shipping address, pick it up and declare it at the border. Went in and showed them my PAL, paid the hst and off I went. Customs did not even look at or in the box. As for Homeland Security, an airgun in the state of Minnesota is a non-firearm and therefore a non-issue for homeland security. Check the appropriate state laws. In my research, I found that some states have a 700 fps "limit" on airguns. While I am unsure, I would think that an airgun with a muzzle velocity of 1000fps would be regarded as a firearm, and therefore under the jurisdiction of homeland security. I didn't go any further in my research since Minnesota law lets me do my import thing. All this is just my opinion. If you do this and get crapped on by homeland security, don't go blaming me. I suggest you call USA customs, tell them what you want to do and ask them if that makes you a criminal.
Canada Customs asked me a few questions about silencers. I imported a Crosman Fury that is advertised as having a muzzle brake. It is simply a cocking handle. There are a few threads on here that talk about silencers on air rifles. I only bring this up because it seemed to be an issue for Canada Customs. Customs Officers were excellent and just doing their job. When I handed the Pyramid Air receipt to the Customs Officer, he immediately went to the Pyramid Air website and looked up the fps rating to determine if it was a PAL-rated gun. Gotta say, everything went so smoothly, I was out of there in under 5 minutes.