I think it's reasonable to presume that any territory added to a country will become the average of that country over time.
So the better question is actually why is the average American such a violent criminal compared to the average Canadian? Answer that and you will have answered your question.
Likely lack of healthcare (desperation), lack of affordable education, debt, need to fill for-profit prisons, corporate lobbying to make regular people's lives worse, etc. etc.
> Violent crime in the US is not evenly distributed.
Neither is it in Canada.
If you want to cherry pick the "best" of the US and leave out the worst from any comparisons, you'd have to do that for whatever country you're comparing it to.
> what would send all the criminality to that province?
Nothing would "send" criminality there, over time any place joining the USA would become the USA, and by definition it would become the average of the USA (because it will be a part of the USA)
A lot of people like to think a place will become the USA in all the perceived "good" ways like higher potential salaries, lower income taxes, more freedom, etc., but they fail to realize a place will also become the USA in all the ways that make the USA so vastly different from every other developed nation (healthcare, education, violence, crime, etc.)
Of course it does! Those higher crime areas are using up limited time and money that could be better put to use making your life better, but instead it's being used to deal with all that crime and criminals.
Rape: 16x higher
Total Crime: 5x higher
Murder rate: 3x higher
Prisoners per capita: 6x more
.. and it goes on
... would you want your community to change like that ?
https://www.nationmaster.com/country-info/compare/Canada/Uni...