You're afforded for legal protection bringing in real firearms into Canada. Clear legal provisions exist for individuals bringing their legally-owned guns into and out of Canada. No such thing exist for replica firearm. And you'd be running the gauntlet twice, once in and again on your way out.
And no, "but you let me bring them into your country" is not a valid defence for getting them back to the US.
"The Bird of Hermes is My Name, Eating My Wings to Make Me Tame."