Rockstar has not confirmed that Michael, Trevor, or Franklin will appear in Grand Theft Auto VI. The only confirmed characters are the two leads, Lucia and Jason, as shown in the trailers. No other returning characters from previous GTA titles have been announced, and the story details remain largely under wraps.
Reports and fan speculation have suggested possible cameos, but these are not backed by official sources. The game is set in Leonida, a fictional state inspired by Florida, and the narrative appears focused on new characters. Rockstar has not commented on the possibility of legacy characters appearing, and no leaks have reliably indicated their inclusion.
For now, treat any claim about Michael, Trevor, or Franklin as rumor. If you are hoping for a crossover, the only confirmed content is the single-player story with Lucia and Jason. Keep an eye on the official trailers and character pages for any future announcements, but do not expect confirmation until Rockstar provides it.