General Brazilian
resposta inesperada
Most common and widely understood across Brazil
São Paulo
resposta inesperada / resposta de surpresa
Standard usage with occasional colloquial variations
Rio de Janeiro
resposta de surpresa / resposta que ninguém esperava
More informal and conversational phrasing
Portugal
resposta imprevista / resposta inesperada
'Imprevista' more commonly used in Portugal than Brazil