I would emphatically avoid defending the wonders of cannabis. I seriously doubt you will make a true believer of her, so avoid that route entirely. Certainly don't make her sit through a presentation, I know I'd find that to be patronizing on any subject and I imagine most other people would too - and there would be no reason for her to even pay attention, since I doubt she gives a shit.
If you think you can argue convincingly that your usage is reasonable, then find the very plainest way to explain it with the fewest talking points. If your usage is responsible recreation, then do what you can to reassure her that it is responsible and explain what you will do to keep it from interfering with your regular life. Think about things like where you will use it, when, where you will store it, etc, so if that's a concern to her you have a good answer ready.
Avoid appearing highly enthusiastic about cannabis. I've found this is a pretty big turnoff for most nonusers, it just confirms too many stereotypes.
If you're vaping, I would point this out IF you're using a non-glass, non-butane vape, as this will appear less antisocial than smoking a pipe or joint. I would not show her your fancy dabbing setup or glass/butane vape if you have a choice, to an outsider this looks like you've managed to make hippy herb into crack. You should emphasize the less-smelly, healthier nature of vaping if you can go this route, since her concern is mostly going to be how it impacts everyone else. If you are into dabbing I'd probably break that news to her after she's gotten used to cannabis use in general, if ever. Probably she doesn't give a damn and assumes it's joints until you tell her otherwise.
If that bridge isn't already burned, my excuse for not telling her sooner would be that I was making up my own mind about whether I wished to use before bringing it to her, or something along those lines with the key point being that you intended to tell her (which I hope is true and therefore not even a lie, right?). If you already goofed this up, just apologize, say you were an asshole, and consider buying gifts in the near future if that's something you guys do.
For now, your goal should be to first of all patch things up with your wife, and second to hopefully come to an understanding for the time being. If you dream of her being truly accepting of it in the future, the best way to accomplish that is to be an exemplar yourself. If she is ok with you continuing for now, then in the future you will presumably have much stronger ground to stand on when you say that you use responsibly and that it is both innocently enjoyable to you and harmless to others, since she will have seen you carry on without incident for some time.
