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

Yes

The word "maratonas" is identical in spelling, meaning, and grammatical function in both Brazilian and Continental Portuguese. The only difference is in pronunciation. In Brazilian Portuguese, unstressed vowels (such as the "a" in the middle or at the end of the word) tend to be more reduced or "swallowed," whereas in Continental Portuguese, these vowels are often articulated with a different rhythmic emphasis or more closed sounds.

Brazilian Portuguese Examples

1. Adoro maratonas de séries no fim de semana. (I love series marathons on the weekend.)
2. As maratonas de rua exigem muito treino. (Street marathons require a lot of training.)
3. Fizemos maratonas de filmes de terror ontem. (We did horror movie marathons yesterday.)
4. Essas maratonas de jogos são muito cansativas. (These gaming marathons are very tiring.)
5. Ele participa de várias maratonas todos os anos. (He participates in several marathons every year.)

Continental Portuguese Examples

1. Adoro maratonas de televisão no fim de semana. (I love television marathons on the weekend.)
2. As maratonas de desporto exigem muito esforço. (Sports marathons require a lot of effort.)
3. Fizemos maratonas de cinema ontem. (We did movie marathons yesterday.)
4. Estas maratonas de videojogos são muito cansativas. (These video game marathons are very tiring.)
5. Ele participa em várias maratonas todos os anos. (He participates in several marathons every year.)