In portuguese we have : first singular person eu pudesse, second singular person tu pudesses, third singular person ele/ela/você pudesse. Portuguese people always use the third person "você" instead of "tu". The second singular person is rarely (or never) used. For this reason it is better to say "...que você pudesse mostrar interesse". Saying "...que tu pudesses mostrar interesse" is grammatically correct, but not used in Portugal or Brasil.
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My portuguese mother tongue teachers have always said that portuguese people prefer using "você" instead of "tu". I don't know if they were wrong, but this is what I learned. Anyway Brasilian people always use "você".