NFA guns are generally prohib in Canada, except for SBR's (if you try to export an NFA firearm the answer will ALWAYS be NO, from USDOS). If you're trying to import a Colt 16 inch AR15 into Canada from the US the answer will be no if the following things apply; the rifle is calibre marked 5.56mm or 7.62mm, the rifle has a flash hider which is screwed on to a threaded barrel end, the rifle has a stock which telescopes. These rifles are not exportable from the US. Any AR15 type rifle, no matter how compliant WILL require an import permit from DFAIT and an export permit from USDOS. If, by De-registered NFA - you mean it was full auto in police service and they have converted it to semi, the answer will be NO from DFAIT as the firearm is a 12.3 prohib. In addition, if the rifle crosses the border with magazines that contain more than 5 rounds, as soon as you are in possesion of the rifle and magazines, you are guilty of an offence punishable by 5 years incarceration or a $5000 fine or both. Y'all have fun now.