Is the word quantos the same in Brazilian and European Portuguese?

Yes

The word "quantos" is identical in both Brazilian and Continental Portuguese regarding its meaning, grammar, spelling, and primary function as a masculine plural quantifier or interrogative pronoun. The only difference is in pronunciation: in Brazilian Portuguese, the unstressed final "o" is often reduced to a "u" sound ([ˈkã.tus]), and the phonetic rhythm is generally more open, whereas in Continental Portuguese, the pronunciation may involve different vowel tensions and a more closed phonetic delivery.

Brazilian Portuguese Examples

1. Quantos livros você comprou? (How many books did you buy?)
2. Quantos alunos tem na escola? (How many students are there in the school?)
3. Quantos dias você vai ficar aqui? (How many days are you going to stay here?)
4. Quantos irmãos você tem? (How many siblings do you have?)
5. Quantos reais você precisa? (How many reais do you need?)

Continental Portuguese Examples

1. Quantos livros compraste? (How many books did you buy?)
2. Quantos alunos há na escola? (How many students are there in the school?)
3. Quantos dias vais ficar cá? (How many days are you going to stay here?)
4. Quantos irmãos tens? (How many siblings do you have?)
5. De quantos euros precisas? (How many euros do you need?)