Who did plantation owners look to for cheap labor?

All we can say is "What are you talking about?" Plantations have always been a thing, and getting labor has always been a thing.

I was surprised to learn that the most common language in Hawaii, after English and Spanish, is Tagalog, not Hawaiian. It turns out Hawaiians don't want to work the plantations, so they imported Filipinos, and they speak Tagalog. Now the Hawaiians are annoyed because their customs and language are being replaced by Tagalog customs and language, so they want to import Mongolians to do the work.

In USA a lot of farm work is done by Mexicans, but Americans are getting wonky and demanding to close the borders. So the Mexicans can't go home, and their population is rising, which is exactly what the border closers were afraid of.

In Australia, about 40% of fruit is picked by foreign tourists on working vacations. So the officials got a bright idea and enacted a tax on non-resident labor. So they refused to work, and now the crops are not getting picked.

This insanity goes on all the time everywhere.

If you owned the slaves it could not get any cheaper.