Mmm, both spellings seem valid., although on google 'cercyon' is twice as common as 'kerkyon'
Both Curitiba and Kurbita are valid but on Google Cuitiba has 32 million entries whereas Kuritiba ahs fewer than 3000. Kurbita seems to be the Portugese/Brazilian spelling.
My money is on Curbita, but I know crossword setters can be unpredictable.