I would say only 2 and 3 are correct. In English you can only use certain nationalities as nouns. These are generally those that end in -an (You sound like a Canadian, Brazilian, German etc). For other nationalities you would have to use it as an adjective and add a noun after, such as guy, person etc (You sound like a Chinese person, French Person, Portuguese person etc). Using these nationalities as nouns is a very common mark of a foreign language learner.
*EDIT: There seems to be some lively discussion as to the validity of sentence 1, so I just want to qualify that my comments are based on my own experience in my region as a native speaker. For me, "You sound like a Chinese" makes it sound like the person is being offensive or is not a native speaker, however it's entirely possible this is a valid construction in other regions!