Unionize rhymes with:
communize, africanize, agonize, aluminize, americanize, antagonize, balkanize, canonize, carbonize, christianize, colonize, communize, demonize, disorganize, euthanize, galvanize, harmonize, hellenize, homogenize, humanize, ionize, lionize, mechanize, organize, patronize, reorganize, revolutionize, scrutinize, suburbanize, synchronize, urbanize, womanize
Unionize sounds like:
umansky, umass, unanimous, unease, uneasy, unesco, ung, ungo, unhinge, unhook, unigesco, union's, unions, unions', unique, unisex, unisys, unisys', unisys's, unix, unmanage, unmask, unos, unwise, unz