The answer resides within Canadian gun laws. I'm not an expert regarding this matter but this is my layman's understanding of it. For the most complete and accurate answer research Canadian gun laws.
If an airsoft gun fires lower than 407 fps on 0.22 gram bb's it falls into the category of a "controlled firearm". These airsoft guns must have "clear" receivers, or at least the half of the receiver that the serial number is printed on for the real steel version needs to be clear.
If an airsoft gun fires above 407 fps on a 0.22 gram bb's it falls in the "uncontrolled firearm" category and has no restrictions involving clear, black or metal receivers.