Cohen's characters are never sutle, and this is no exception.
Rather than North and South, the parody is about rich and poor. Two brothers separated as children, one is adopted and has a priviledged upbringing, and the other, a normal (working class) upbringing. The extreme differences in their paths is exaggerated for comic effect.
If you want a debate about the North /South divide, try framing it about the wealth gap, employment opportunities and prosperity. Not about migrant intakes, and comedy.