Rockstar has not confirmed any real car brands for GTA 6. The game will feature vehicles, as seen in the trailers, but no licensing deals or brand names have been announced. Historically, GTA titles have used fictional vehicles inspired by real cars, and there is no indication that GTA 6 will break that pattern.
What is known is that the game is set in Leonida, a state modeled on Florida, and the trailers show a variety of cars, boats, and aircraft. However, the exact vehicle list, including any real-world brands, remains unannounced. Reports and speculation suggest Rockstar may continue with fictional brands to avoid licensing costs and maintain creative freedom, but this is not confirmed. The vehicles page on this site tracks all confirmed details.
For players, this means you should not expect to drive a specific real-world car in GTA 6 at launch, based on precedent. Rockstar has not said otherwise. Watch for future announcements, possibly in a third trailer or gameplay reveal, which could clarify the vehicle roster. Until then, treat any list of real brands as rumor.