I would agree with Monsieur Ménard.
I agree with your question and your analysis: the form is the responsibility of the provinces and the substance is a matter of federal jurisdiction. However, the federal government has set the minimum age at 14 because of other sections in the Criminal Code. You are correct on that point.
Let me go to a scenario that I think I've thrown out before. In this scenario, that would be a crime under this section once it's in force, because you have a larger age gap than the five years.
Let's take a 15-year-old and let's do the stereotypical relationship of a young woman who is pregnant, with a male person who is 21. There's an application to the court, by way of consent from the parents of the girl. The parents have said they're prepared to allow this to go ahead. This is a relationship that they are prepared to acknowledge as a marriage. They apply to a court—this would be the scenario that you'd go through in Ontario in any event, or you could go to the minister in Ontario—and say this is the situation. They want this to be acknowledged by the state as a valid marriage, and they need the permission of the minister to do it. The parents are consenting, so would the minister consent as well? If he or she does, then the marriage is allowed.
If that scenario developed, it would now be in direct conflict with this law, and there's no question that the federal government has the jurisdiction once they occupy the territory. That's really what's happening here. It hasn't been occupied to this level, so we have effectively allowed the provinces to fix the age of marriage up to this point. We are now doing that at the federal level, with the age of 16 being a minimum age.