Why do Malaysians have Cantonese surnames?
Historically, there were waves of emigrants from Southern China to Southeast Asia since 明 dynasty (1368-1644). So, their descendants shared the same Cantonese, Hokkien surnames with people in Southern China.

Then, the British empire acquired Hong Kong &amp; Malaysia in the 18th century. Both governments used the same / similar romanisation scheme to register people's names in English. That's why Malaysians with Chinese origin would have a Cantonese / hokkien surname, as those in Hong Kong.

As far as I know, there are subtle differences:

陳 - Chan (hk), Tan (my)

黃 - Wong (hk), Ong (my)

Edited, adding info:

Several books, in literary Chinese, had info about Southeast Asia &amp; China:

東西洋考

西洋番國誌

瀛涯勝覽

星槎勝覽

Read between the lines, you'll grasp the ideas :)