Hello James! Interesting questions, and sadly, ones to which I do not have direct answers. However I can give you a few points to ponder, which might have some influence on your side of the discussion.
First, under the generally accepted rules of debate, if you make a claim that "studies show" or that something is what you claim it is, it is up to you to provide the proof.
Is it the case that there is scientifically supported data saying that there is a strong correlation between men who commit spousal abuse and those who commit mass-shootings?
If he is claiming scientifically supported data, then he should PRODUCE it. Or, at the least, give you a way to find it on your own. (an link to the study, or its name, at the least...)
another point, what is a mass shooting???
At one time (in the US) the FBI counted it as a mass shooting only if 4 or more people were KILLED (which could include the shooter).
Today, the press reports 4 or more people SHOT as a mass shooting.
Shot, not killed. This has a huge impact on the number of shootings that fall into the mass shooting category. If you wonder why the number of mass shootings has ballooned up hugely in recent years, this might be the explanation. (some years back, our doctors changed their definition of obese, and suddenly a huge segment of the population that had formerly been simply overweight was now classified as obese, and we had an obesity crisis!)
The next point is the phrase, "a strong correlation". First, what constitutes "strong" can be entirely a matter of opinion. But more importantly, correlation is NOT causation. CO-RELATED, meaning that there is something in common between the two things. The usual (and minimum) thing they have in common (no matter what correlation you are discussing) is that they are found in the same place, at the same time.
Nothing more is needed for someone to claim a correlation. And be correct that there is a relationship. However, the technically correct claim of a correlation is very often used to IMPLY that one causes the other, or that the presence of both together causes a certain behavior. This is not necessarily true.
One could produce a "scientifically" valid study showing how the overwhelming majority of mass murderers ate bread, or a bread product within 30 days of committing their crimes. it would be TRUE, and scientifically provable.
However, claiming (or implying) that eating bread is the cause of mass murder is a fallacy.
Next point, the phrases "more likely to"... and "at higher risk"...
What does that mean, exactly? It is often used to warn of some grave danger or risk, without any kind of specifics.
These phrases are open ended, and very, very seldom used with the actual numbers that might allow one to actually assess the degree of likelihood.
They don't tell you that something is 73% more likely to happen, or just 2% more likely, they leave the numbers out, to allow for people imagination to assume the worst case possible. It is deliberate.
These are a few of the points one ought to consider whenever "studies show" is mentioned. AND, they apply to both sides of the issue. I think our side of the issue generally does a better job of using the truth than the other side does, but of course, the other side thinks they are the good guys, too...
As to what happens in Canada, I cannot say, I don't know the Canadian laws in detail, but I do believe their system included magisterial discretion, meaning that at some point, it is up to the local magistrate's opinion whether or not to issue a license, and each individual magistrate can have differing requirements as to what satisfies their concerns.
In other words, magistrate A might require spousal approval before issuance of a license, while magistrate B, in the next province might not.
Hope this helps with your arguments.
