Hi, American sports are shown on television. But you would probably have to go to a sports bar to have a chance at seeing the games. The regular state television channels show only Cuban, Latina American and some European sports. Sports bars sometimes have international signals and show American sports. Maybe try the sports bar on the mezzanine level in the Hotel Nacional. I’ve seen some football there. You would have to ask the bartender to check the channels for you.
Specifically about the NCAA tournament, honestly, basketball is not big in Cuba. If there is any soccer or baseball game at that time, you can be sure the tv will be tuned to the soccer or baseball. But, it doesn’t hurt to ask the bartender to check or play the basketball, if they have it.
But in general, I would put the chance of you actually being able to watch a tournament game in Havana at less than 25%. Good luck!
Mario