Flintlocks do not have to be registered in Canada (unless it is a pistol and thats a whole diffferent story). Just buy them, declare them and ship them. Must be shipped via an authorized firearms shipper or carried across the border and given to the new owner.

Other firearms need to be registered and are generally shipped via brokers here in Canada. I'm not sure of the regulations on private sales.

More info can be found here;

http://www.cfc-cafc.gc.ca/pol-leg/FireArmsAct_e.asp

and

http://www.cbsa-asfc.gc.ca/menu-eng.html