That is an Americanism, but you also failed to grasp what I pointed out above, it also works against Native Canadians when they are the accused and the crown makes the peremptory challenges.
It's not an Americanism its a Britishism that dates back to the Magna Carta. It comes from Common law, where both American and Canadian law originates.
And the whole idea of the peremptory challenges is to weed out people who might be racist or biased against or in favour of the accused.
Reading up a bit on this, there were originally 35 such challenges allowed in Britain, but the number was lowered over the years to a handful and has now been abolished there. They've gone back to 'you gets what you gets', or a random sampling of the population.