A Correction
I must correct an error in my own previous post:
As FLYDCA points, there is indeed this flight JJ3748 which is usually flown with a widebody (332/767/777). This aircraft has a separate business class cabin, and it is, to my knowledge, the only one (internal) flight in Brazil to have it.
To JJBe; if you were in this flight and the aircraft was changed to a narrowbody without business class cabin, I believe you really are due some compensation; at the minimum the fare difference.