Fellow Canadian speaking here: from what I've seen in the depressing amount of and reactions to gun massacres in the United States, the reason for the gun problem lies in a complex web of sociopolitics, the arms industry, a lack of weapon regulation, the drug war, and uniquely American culture.
On one hand: culture plays a significant role. There are far too many citizens in the U.S. that fetishize the hero complex, firearms and self-defense to an utterly fantastical degree. They will cling to their weapons because they see an attempt to "take them away" through utterly pedestrian regulation as a direct assault on them, and they will vehemently resist so (incidentally, these people have an awful lot of crossover with the "Cold Warriors": Reagan-era conservatives who believe in an American military supremacy born from living through the conflict with the Soviet Union). You will almost assuredly never convince these people that their love for firearms is both unhealthy and nonsensical (my laptop is essential to my job and livelihood: I don't pose naked with it and run my tongue along it), short of them actually becoming or being close to victims of gun violence themselves. What you can do is start fostering a broader cultural shift that emphasizes rehabilitation of criminals, societal investments and public spending to make people feel safer in their own homes.
On the other hand: regulation, or lack thereof, plays a role too. This level of violence just does not happen in other developed nations, and there is more than a little evidence that correlates the presence of firearms in a society with deaths by those firearms. This is particularly prevalent with suicides: people are less likely to kill themselves when you make it more difficult and timely for them to do it. Or, put in a different way: the only reason that the Planned Parenthood killers were using lousy, homemade pipe bombs was because they couldn't go to their local, friendly military dealer and buy RPG's with no checks involved, and if they had, many more people would have died. So, to curb this, you put in mandated licenses, universal background checks, a national gun registry and waiting periods. Implementing a national buyback of firearms will also get a good portion of the 300 million-odd guns off the ground and make it easier to track loose weapons. Most importantly, you mandate firearm training for all license applicants, and include a section on how to properly store their weapon, which curbs the rate of accidental deaths.
There are multiple other factors. The drug war certainly increases street crime which bloats gun death statistics. The gun manufacturing industry and the gun lobby has a heavy presence in Congress, and politicians refuse to stand up to them because they know that a "Your congressman hates YOUR GUN!" ad running in their state by an opposing Super-PAC will mean the end of their political career. But the broader point is that this can't be traced to one issue, and you need to address every facet at once if you want to fix it. That includes regulation, that includes a cultural shift, and that includes drug and campaign reform.