Vietnamese are diverse people. Some can are closer to Cantonese and Some are closer to us. Lanna and Lao are more likely related to the Vietnamese living near the South China borders. 

@dyno 

I think it's called "Ancient Coastal Southern Chinese"

Quote from a study:

When we analyzed the DNA of people who lived in coastal southern China 9,000-8,500 years ago, we realized that already by then much of China shared a common heritage. Because their archaeology and morphology was different from that of the Yellow River farmers, we had thought these coastal people might come from a lineage not closely related to those first agricultural East Asians. Maybe this group’s ancestry would be similar to the Tianyuan Man or Hòabìnhians.

Actually Igorots of Northern Philippines are the only pure Austronesians resembling the Ancient Coastal Southern Chinese population. According to this latest Philippines study the Igorots/Cordillerans were hunter-gatherers rather than agriculturists:

Multiple migrations to the Philippines during the last 50,000 years | PNAS

Present-day Cordillerans, however, do not display this nEA ancestry component (SI Appendix, Figs. S2 B–D and S9 D, E, and J and Tables S8 V and X), thereby providing a minimum bound for the divergence between Cordilleran-related groups and ethnic groups of mainland East Asia and Taiwan at ∼8,000 B.P. This finding, taken together with the earliest archaeological evidence of Neolithic assemblages dated to ∼3 to 4 kya in the northern Philippines (21), suggests that the earliest Cordillerans were, like other groups in coastal East Asia at this time (22), complex hunter-gatherers rather than settled agriculturists. The nEA ancestry must have arrived later, originating from the coastal China/Taiwan area and dispersing into Batanes Islands and coastal regions of Luzon (SI Appendix, Table S8X). If the presence of nEA ancestry is indeed a genetic signal for the spread of agriculture, its general absence among Cordillerans suggests that the Neolithic transition among these groups was a consequence of cultural, rather than demic, diffusion.

Urban Filipinos on the other hand are more mixed with other populations:

@j-r-c Most of the Vietnamese are closer to us I believe than to the Chinese Cantonese. 

@cheesefries Igorots are not too different from the rest of the population.