here in Canada they would be fucked and they would have had the legal duty to retreat.
Yes, Canada prosecutes victims of violent attacks for not running away fast enough, and causing harm to their attackers.
Generally speaking, the US does not. In most of the US (36 of 50 states), we have legislatively affirmed that the victim’s decision to meet force with force is unassailable. The presence of a potential means of retreat does not negate a self defense claim; the victim is free to do anything they believe necessary to end the threat posed by the attacker. Our license to use force ends when the threat ends.
That is a power we claim for ourselves, and not one given solely to our cops.
No, what Canada has done right is enacting a stronger social safety net. Universal healthcare, for example. Your citizenry has a greater expectation of aid and comfort than ours, and that has translated to much less of the kinds of desperation that drive criminal activity. The US certainly has many things to learn from Canada, but “duty to retreat” is not one of them.