No, not all. Just the majority. There were a minority of Chinese from other parts of the country who went to America in the early waves of immigration. For example, people from Fujian.all earlier chinese that go to america are cantonese descent.
Additionally, I have seen evidence of some Chinese from Shanghai going to North America. For example, on page 46 of the book 'The Chinese in Latin America and the Caribbean' (ed. Walton Look Lai, Chee Beng Tan) it claims that "Two of the three French vessels which sailed to Martinique and Guadeloupe in the 1860s also recruited their passengers from Shanghai, rather than Guangdong or Fujian."
Edit: By the way, I forgot to mention that there is speculation that Ho Chi Minh spent some time in the 1910s working in New York City, which would have made him one of the earliest recorded Vietnamese immigrants to the USA if it is true.