This is a tough one. I think each fighter would win some rounds and Gervonta would try and rely on the counter against a pressure fighter like Marquez, but similar to Cruz did - Marquez would be effective at piling on the pressure and land enough shots to win the decision. One of those fights where Marquez really wins but Gervonta gets the judge's nod. Although it is a close one.
JMM always performed well against southpaws, especially aggressive ones. Tank’s style would play into JMM’s counters, although he’ll most likely drop him at least once.