Indeed, the acoustic guitar is almost like our national instrument...
Most of our popular music, like Choro, Bossa Nova, Samba, and so on is based on the guitar. Tom Jobim was not only a very talented pianist, but also a skilled guitar player... Even Heitor Villa-Lobos, although a serious cellist, played and loved the acoustic guitar and its existing music.
As for the music itself, I think samba is the rythm that was best mixed with jazz, giving birth to Bossa Nova, my personal favourite Brazilian music.
My apologies if my English is a bit rusty
Cheers, mates!