I did a measure-up once of a v3 gearbox against an Armalite... unless you want your receiver to NOT look like an Armalite... then you won't be jamming a v3 gearbox in to an M4 or M16 any time soon.
As for manufacturing replicas in Canada - there's something you may have heard of called "copyright law" that's pretty heavy-handed and well-enforced in Canada. I'm sure the cost of that legal suit will cost you WAY more than any money you'd make or save off manufacturing that part.
Why can metal parts be replicated/manufactured in Taiwan with near 1:1 precision? Because Taiwan is a copyright black hole. For whatever reason, international copyright law doesn't apply in Taiwan - they can't be touched.
As for replicas made in China? That government is so corrupt, as long as local enforcement is paid off, they'll turn a blind eye.