Open borders simply means people can travel freely, similar to the Schengen Area [1] in western Europe. It doesn't mean they have some sort of automatic dual-citizenship or whatever it is you're talking about here.
The Schengen Area is relatively uniform with regards to government subsidization of healthcare and the availability of guns.
The same can't be said of the US and Canada. The incredible amount of regulatory capture in the US makes them unlikely to reconcile those aspects of their society with the rest of the developed world any time soon.
Setting aside your subjective opinion about the state of the US's government, the Schengen area includes countries such as Slovakia and Austria. Apparently there have been no wave of Slovakians migrating into Austria despite the gap between their living standard, political transparency or corruption level. Hungary and Austria for that matter, or Poland and German. The agreement is only about open border. Nothing else.
You clearly fail to understand the statistical differences in health and safety between those countries if you think they’re comparable to the gulf that exists between Canada and the United States.
[1] https://en.wikipedia.org/wiki/Schengen_Area