I bought an unlocked iphone in dubai and i will use only in Brazil. I will be able to use facetime?

If you have a sim with internet yes 🙂

No you will not. iPhones sold in the UAE and Saudi Arabia have facetime permanently disabled as required by law in order to be sold in those countries. Your Dubai purchased iPhone, if purchased from an official Apple Authorized reseller will never have facetime. The SIM card has absolutely nothing to do with it.

Since FaceTime is banned & removed from all iPhones sold from official sources in the UAE, if purchased from an official source, your phone won't have FaceTime & there's no way to add it back.

If your phone does have FaceTime, that means it's a grey market import, & could have originated from who knows where, & may have been hacked to unlock it.

Good luck.