As a Brazilian, not much. Throughout my entire lifetime, I saw some Brazilians there and there wearing Halloween costumes but it’s not as popular here as “quermesses” (kirmess, church fairs, happening mostly on Brazilian’s interiorian towns), Carnival, Christmas or some “important” soccer game (such as Corinthians vs Palmeiras, or Flamengo vs Fluminense).

To me, particularly, no holiday (nor soccer games) holds any importance or meaning. In the end of the day, it’ll be just capitalism mesmerizing people to spend money on temporary things.