The Wikipedia entry on Kanaka says (among other things),

"Kanaka", originally referred only to native Hawaiians, from their own name for themselves, kanaka ?oiwi or kanaka maoli, in the Hawai?ian language. In the Americas in particular, native Hawaiians were the majority; but Kanakas in Australia were almost entirely Melanesian. In Australian English "kanaka" is now avoided outside of its historical context, as it has been used as an offensive term.

Wikipedia goes on to say,

According to the Macquarie Dictionary, the word "kanaka", which was once widely used in Australia, is now regarded in Australian English as an offensive term for a Pacific Islander. Most "Kanakas" in Australia were people from Melanesia, rather than Polynesia. The descendants of 19th century immigrants to Australia from the Pacific Islands now generally refer to themselves as "South Sea Islanders", and this is also the term used in formal and official situations.

I note that I've never heard anyone in Australia sing it as "John South Sea Islander". About the use of the word "immigrants" in the preceding paragraph, Wikipedia clarifies:

Most of the original labourers were recruited from the Solomon Islands, the New Hebrides (Vanuatu), and New Caledonia, though others were taken from the Loyalty Islands. Some were kidnapped ("blackbirded") or otherwise induced into long-term slavery or unfree labour.

I think this lets the "recruiters" off lightly, but I claim no expertise on this.