Why "We're" is used in here. I though it should be "We will".
Answer from a Native speaker
"We're" is used here because this sentence is in present progressive tense, which combines "am", "is" or "are" ("be" verbs) with an -ing verb (present participle). In this sentence, "are" from "we're" is combined with the present participle "flying". Present progressive tense is used here to describe plans in the near future, which are "flying to Rio". "We will fly to Rio" can also be said. Examples of present progressive tense: Ex: I am riding a bike. (This is happening in the present) Ex: He is working on a project. (This is in progress) Ex: My friends are going to the movies this afternoon. (This is happening in the future)