I’m honestly surprised they haven’t brought up her Canadian background.
By referencing her Canadian background, they can subtly frame her as being “exotic” and “foreign” and “liberal” in a way that doesn’t sound racist (but which would provably still resonate with racists).
Also, “Canadian Kamala” has good alliteration. I could imagine Trump using it.
Second of all, I genuinely think Canadian Kamala might be too long for Trump and his followers. A good alliteration sure, but I could more see him using something simpler like Killer Kamala, after finding (or more honestly making up) a reason to use it.