People who call themselves cantonese and not chinese are mostly from Hong Kong. People in Hong Kong always thought of themselves as superior to mainland Chinese and not just that they openly discriminated against them and darker skin people from south asia many of whom hold Hong Kong passport.
If you want to talk about regional differences like Newyorker or Californian then it does exist in China today where Shanghainese consider themselves at top and mostly disliked by Beijinger or HongKonger and others.
Efforts for unification of China started in Qin empire (221–206 BC) [0], which includes language standardisation and still a work in progress given there are still large number of dialects and ethnic groups in China. Lucky for China many of its historical culture remains along with language, cannot say the same for native Americans, whose language is not even part of official languages in North or South America.