This is a very interesting subject. The term you are looking for seems to be a term used in sociology. In the links you sent, the term sugar grower is alluding to the farmers that grew/cultivated/planted sugar cane in Southern US during the civil war. Strictly, cultivador nowadays is used mainly for agriculture machinery (http://www.fao.org/faoterm/es/) and productor for the person growing or planting the crop. I looked up the term from a sociological point of view and it seems "plantador" would be generally accepted for the historic context . Extrapolating the use of the term in South America, "cañeros" is a term used to refer to the "powerful" sugar cane growers. I didn't find references to plantador de azúcar, only to plantador de caña or de caña de azúcar.

More references in the US historical contex:

thttps://books.google.com/books?id=8MnmAAAAMAAJ&pg=PA425&lpg=...

https://books.google.com/books?id=KfG5DwAAQBAJ&pg=PT38&lpg=P...