You will need a business licence from your municipality, if one is required, and a shingle out front proclaiming your new profession. From there, skills and business accumen (and the ability to survive on very little food) will be the tell as to whether you make it.
There are, as far as I have ever found out, no certifying requirements, although Ontario apparently requires that you have passed a recognized course, without actually defining by who or how it should be recognized.
Talk to the CFC about their requirements.
A couple sizes of hammers, some cold chisels, a bench grinder, you should be good to go!

Maybe a welder of some sort.
Seriously, though. Some machining skills would be really useful. Welding. Skills with hand tools. Business skills. Woodworking. It really is a trade that requires a broad spectrum of skills that may or may nt be called upon in a given day.
Books. Gunsmithing, by Dunlap. Modern Gunsmith by Howe. Two standards. The business environment has changed a bit, the tools and parts available, and especially the reference material available, has changed hugely since the times these books were written, but the skillsets are pretty much the same, if one is not looking at modern military style firearms.
Decide what you want to do. Storefront. Custom builder. Benchrest. Hunting. Shotguns for Olympic shooters. Tactical. Bunch of different ways you could go. Gotta choose a path. Stckmaker. Checkering specialist. Engraver. And on and on and on.
"Gunsmith" is like "Cook". It covers too much ground to really be able to claim you are good at everything.
Cheers
Trev