Policies for USPS and UPS and FED X
All three ship firearms. All three ship firearms parts. Long guns can go ground, hand guns go two day. that's a carrier policy, not a BATF. (FED X and UPS both do this if I recall correctly)
If you get static at the counter, get the manager. If you still get static, get his/her manager. The only way these clowns will ever get the message is by making them stick to policies. This isn't a privilege, it's a constitutional right. . .
Now, of course we know that we must be good little minions and only ship whole guns/receivers to those who have FFL's. Gun parts other than serialized receivers are just machined bits of metal and are of no concern to anyone.
As for Canada. I don't know your laws bud, sorry. Seems to me though that I've shipped and received stuff from there without any drama.