Rumours of Mafia 2 and 3 remasters are becoming legitimized through rating boards and the official announcement is expected to come along any day now.
Taiwan Digital Game Rating Committee has rated Mafia 2: Definitive Edition and Mafia 3: Definitive Edition. While the third one is the black sheep of the family, the second game is beloved by many and the Definitive Edition will likely be a welcome addition to many libraries.
Coupled with the news of Take-Two trademarking application, these versions of each game are all but confirmed. Technically, no one explicitly stated that the DE will be a remastered version of Mafia 2 but it would not make much sense re-releasing a 10-year-old game without bumped up graphics.
As for Mafia 3, that game was a step down from the previous title in the series in more cases than just the graphical fidelity so the fans would prefer a rework rather than just a remaster. Whether anything along those lines becomes reality is to be seen but holding one's breath may not be the best course of action in this case.
In case you didn't play Mafia 2 or simply want another run with Vito Scaletta but can't wait for the remaster, there are plenty of graphics-improving mods that will make the game quite beautiful.
As official info is lacking currently, there is no way of telling when the definitive editions might pop up for either game.