ARs and their variants are specifically designated as 'restricted firearms' by order in council - essentially by an order of the Prime Minister made without consent of Parliament. License, registration certificate, and a specific authorization to transport or carry are necessary before you can go to the range. Shooting with a restricted firearm anywhere other than a range - gravel pits, your field etc - is very difficult or impossible to do legally. Miss a piece of paper and you can expect to be criminally charged and have your entire collection confiscated if you are questioned. 5 rd mag limits apply unless your AR is beltfed, in which case you may fire when ready. Restricted firearms apparently cannot be used for hunting due to their government-declared 'nonsporting' status. Full auto is not permitted unless you have continuously owned a full auto gun since the 70's. Sound suppressors are 'prohibited devices' and may not be owned by a civilian except in rare and heavily regulated exceptions apparently intended to allow for government production. Folding/collapsing stocks, flash suppressors, threaded muzzles, accessory lugs and the like are permitted. Since the guns are already restricted, barrel lengths can be anywhere down to a bit shorter than 5" without changing the legal status of the gun one whit.
The HK SL8, SL8-1, G36 and UMP are all non-restricted IF the specific gun in question was manufactured as a semiauto only and has never been full auto. Exactly the same amount of regulation as a 550 fps pellet gun except that ammo vendors require you to show your mandatory license in order to purchase ammo.
There's much more to our laws, but that gives you some of the basics. BTW Striker I was |\|f/\ prior to the mandatory name changes for users with special characters. I'm a Manitoba director for the NFA. My best advice is to GET IT ON TAPE from 1 800 731 4000 - they might not be right, but at least you'll have the 'official misdirection' defence should it come to that.