Are you referring to a business license, or a specific Gunsmithing trade ticket?
Within my understanding of the law, if you are operating a business, you need a business license regardless of what that business is. If you are in a residential area operating out of your house you can only employ yourself and only if it is your residence (ie you cannot have employees and you cannot live in one location and work at a second location). If you are working on guns in any capacity and receiving payment for it, either you or the owner of the business requires a gunsmithing license, In BC and presumably in the rest of Canada, that means being inspected for security details and keeping records of your work. The license does not imply any level of competence as a gunsmith.
You do not require a gunsmithing license or a business license if you are working on your own guns or if you are working on a friend's gun for free.
cheers mooncoon