US cops ? Well I do not want to defend any of the ones that are clearly trigger happy psychos, BUT I will say this about them:
They have to police a country where anyone they encounter can (thanks to the 2nd amendment) can also be an armed trigger happy psycho. Their police, and even their security guards, have it drilled into them from day one, to approach every person like that person is a potentially lethal threat to their own lives. Psychologically they are on high alert, all the time - one false move and they'll unload a whole magazine on you, (in their minds) before you can unload one on them. Is that reaction aggression, or fear? Probably both.
So add that factor to the racial animosity that's hard-wired into US society, plus the whole jock thug attitude of some cops who just want to hurt someone legally, and what you get is a lot of shootings, beatings, tazerings, etc.
Everything is weaponized. Everything is racialized*. Everything is politicized. "Welcome to the USA." It's a fucking mess, but their mess to deal with.
(*That's what "racialized" actually means, folks. It's about societies where the racial filter is on everything: every person or group is judged by race first, on all sides of the equation. NOT the bullshit misuse of the term that is so common these days.)
Not every US cop is a bloodthirsty goon or a racist scumbag, but I certainly wouldn't trust that they're not either. I would act very carefully around them. Be cooperative, not ever frantic or aggressive. You don't know what's in their head; you don't know what kind of bad data they've gotten about you by way of some panicked 911 call.
Canadian cops? Well, it's less of a trigger-happy thing here because we do not have the same "everyone has a gun" culture (and hopefully never will), so they are not as quick to assume every person they meet is Billy The Kid and gun them down. Still, criminals and extremists up here are increasingly well armed because there's so much surplus weaponry coming over the border - therefore violent capability by the Canadian police must rise to levels which overcome it. That's the thing about cops: they have to come out on top in any forceful confrontation. That's how it has to be. (You do not want to live in a country where police have actually lost control of the streets to criminal gangs.)
To me a big problem is when Canadian cops end up emulating US law enforcement attitudes and techniques. Our cops go down there for special training sessions; they watch videos meant for US cops within US society & full of US assumptions; they go onto internet forums about policing that are dominated by US cops, and therefore full of US attitudes and US politics. Immerse Canadian cops in that for very long, and they will start to act the same way. They get indoctrinated into the attitude that it is an adversarial culture with all cops (good or bad) on one side and all civilians (good or bad) on the other. If "race" is involved in their thinking at all, it's that automatic pre-judgement (prejudice) about whether someone's up to no good, or whether as a victim, their life is worth anything at all.
Policing will always be adversarial between cops and criminals, it has to be. But it does not have to automatically be that way between cops and everybody else. That's the mistake that keeps being repeated.
But this is nothing new - look at just about any organization with any sort of power, and you'll find the same internal struggle, against corruption of purpose and abuse of power.