There isn't a difference. And it's "Qual". "Cuál", would be in Spanish.

Dear W.W, firstly, allow me to correct your ortography : "Qual" instead of "Cual" . As regards your question, there is no difference in the meaning, both sentences are gramatically correct, because the use of definite article, in this case: "o" , before the possessive pronoun, in this case "seu" is facultative .

Spelling mistake. It's "qual" in Portuguese. In this case 'o' means 'the', so both sentences are correct, they have the same meaning. In some places in Brazil, people use articles more often.

The 1st sentence is The only one that we use in Portugal. And you have to write "qual" instead of "cual"