To get stuff form the US the Department of Defence has to approve the export.
Furthermore, besides the incredible bureaucracy you would have to wade through, lots of items are 'sensitive' and not allowed to be exported, EVER. So there went my plans to buy an AR in 6.8mmSPC. It's not allowed to be exported. And .50 rifles, they're too sensitive to be exported.
In essence, the export process is completely controlled, and highly bureaucratized and militarized.
That's just the impression I got. And it's sad, because US prices are great, and Canada's import laws are great, so it could be a winning combination if not for the defence department.