If you are Vietnamese and French with South Chinese background, you probably share the same kind of DNA with Vietnamese people. Zhao Tuo after invaded Nan Yue (Nam Viet) he crossed gene with another Vietnamese princess. Don't worry about your Chinese background. Those Chinese won't treat you good or did not treat you good. That was why your ancestors wanted to run away from that lovely ancestry place. Chinese is just a nationality. When you move out of China, you are no longer Chinese. The Southern Chinese most has common ancestry and ethnicity, the Yue, for a long time ago. If you live in China, you are a Chinese for sure. If you move to the United States, you are an American for sure. Don't worry about the culture since some of the Chinese cultures originated in the North, except for Lunar New Year, Mid-fall festival, and boat festivals. There are more but my memory and knowledge are limited.
http://www.yawningbread.org/arch_1998/yax-125.htm
http://www.hoklo.org/YuetCulture/Articles?item=1
pay attention to the second link, Chinese has two origins, the North and the South. The reason for South Chinese to support their ethinicity as Han was in the past, they were taught that San Shui Huang united all the tribes and later went to South as the Yue. It's up to believe that you are from the North but the anthropologists would do their jobs to say, "Chinese has two origins." That's a hard fact. Believe it or not is up to you.
