Canada is larger, more geographically dispersed and less homogeneous than the United States, and yet manages to have a functioning single-payer medical system.
Not sure what you define as 'homogenous' but over 20% of Canada's population is foreign born, and less than 57% are english speaking by mother tongue.
http://en.wikipedia.org/wiki/Quebec_City%E2%80%93Windsor_Cor...