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

No. There is a difference in typical usage and the meaning of the related term guitarra. In Brazil, violão is the standard word for a 6-string acoustic guitar, while guitarra refers specifically to an electric guitar. In Portugal, guitarra is the standard term for an acoustic guitar, and violão is not used by Portuguese people to refer to this instrument; using it would be perceived as a Brazilianism.

Brazilian Portuguese

1. Eu toco violão na igreja. (I play acoustic guitar at church.)
2. O seu violão é muito bonito. (Your acoustic guitar is very beautiful.)
3. Eu quero aprender a tocar violão. (I want to learn how to play acoustic guitar.)
4. Ele quebrou uma corda do violão. (He broke a string on the acoustic guitar.)
5. O som do violão estava muito alto. (The sound of the acoustic guitar was very loud.)

Continental Portuguese

1. Eu toco guitarra na igreja. (I play acoustic guitar at church.)
2. A tua guitarra é muito bonita. (Your acoustic guitar is very beautiful.)
3. Eu quero aprender a tocar guitarra. (I want to learn how to play acoustic guitar.)
4. Ele partiu uma corda da guitarra. (He broke a string on the acoustic guitar.)
5. O som da guitarra estava muito alto. (The sound of the acoustic guitar was very loud.)