Most of the time you can get your answers just browsing through the forum. But your question is about legality of the firearm - perhaps you meant what makes it non-restricted. If the RFB were to be allowed export from the US to Canada, it would be considered a restricted firearm based on barrel length. The RFB-C has a custom length barrel to meet the classification requirements for a non-restricted firearm (barrel at 18.5" min and 26" min overall length). Any other changes to the rifle, such as the chambering and lack of muzzle brake were done to meet US export regulations, not Canadian firearms legislation.
All that said, the RFB is really no different than my uncle's Browning BAR - Both .308, semi-automatic, 5 round rifles. Optically they are night and day...clearly the Browning doesn't look as "Scary". The more I take my carbines out hunting, the more accepted they are becoming...The RFB may be a game changer, and the reaction by hunters I've shown it to have been great. I bet if it were camo dipped Vault would never be able to meet the demand.... Hmmmm camo dipped....