Smoking is illegal in no state or province.
What is illegal in a slowly growing number of them is smoking in public spaces where most people would prefer to avoid ETS (which incidentally kills nigh double those killed by guns - let alone the 14 times that gun number killed by smoking overall).
Your wish has long since already been granted; initiating a shooting in public spaces is already illegal - actually illegal - in every state and province. Just like you can have your cigarettes with you as long as you don't light them, you can have a gun (in some states) as long as you don't fire it. It's the harm to others in both cases that is illegal, although the mere possession of guns is banned in quite a lot of areas - cigarettes in none.
Now if your suggestion is that some of the campaigns to change societal norms that reduced smoking might also work to reduce gun ownership overall voluntarily, it's certainly possible although slow and limited. Essentially all movies set and made in the 50s showed positive characters smoking. Now almost none do. Removing guns from TV and movie heroes of course means finding something to replace war, cop, western etc genres. PSAs are likely to be less effective than in previous decades due to image saturation, unless they were so graphically shocking as to initiate a serious backlash among the sensitive types. Might be worth trying.
The social shunning of smoke-filled venues and people was more possible because it is obviously very apparent. It's hard to tell a bar or restaurant you'll refuse to go there because of all the gun carriers when you have no idea normally how many there are. So that's probably out. You could start a campaign to encourage the shunning of friends' houses etc if they have guns which may have some impact over time, with the loss of many social networks. Probably the best possibility here would be to convince business owners to post "no guns allowed" signs to keep your patronage. The trouble of course being that you have to be able to deliver boycotts greater than those who will refuse to go in because of the signs. Night get a bit of traction here but be damn sure you have the numbers or that will backfire quickly if it loses them business.
I suspect the most effective tactic is also the most risky and most difficult. Humans are gregarious by nature. A far greater percentage of us follow the herd than would care to admit it. The very existence of fashion proves this, but you don't have to wear Prada to be a follower. Look around the next large public gathering you attend. How many male or female have 80s style big hair? How many are wearing caftans or Oxford bags or mood rings? How many have muttonchop sideburns or fedoras? How many in short have some thing wildly out of styles and norms of the day? The tiny few who you see are the ones who are not followers. Too few to worry about.
So how do you apply this to guns? Stop guns being cool. Remove them from positive or even fashionably negative images. This means either disarming cops or making them carry concealed. Same with military shows and security at airports and the like. Ban open carry (to keep this constitutional, you'd have to allow concealed carry - it does say bear arms after all) for EVERYBODY. The Secret Service manage it - so can the cops. Combine this with movie and TV changes and other stuff mentioned above and, 30-40 years from now, legal, normal citizen gun ownership will probably be a lot lower.
Will that, even then, reduce spree killings? Not sure anyone can say. Certainly not to zero. Guns are durable, cigarettes aren't. Guns provide a real advantage in both criminal acts and self defense, cigarettes don't. Making a publicly obvious habit unpopular is a lot easier than making a powerful and concealable tool unpopular. But absent absurd 2A repeal pipedreams, not sure what else would do much.
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