Not very logical--the risk would have been enormous.

I posted on this a long time ago. One possibility is that Michael needed to keep stringing Roth along with the promise of the $2 million until he found out who was the traitor. As he told Pentangeli, he needed Roth relaxed, confident that their relationship was still good. Having the $2 million brought to Havana was one way to keep that going.

Another possibility (admittedly a stretch): Michael knew the rebels would win. He knew he had to have Roth killed, but he still wanted Roth's Havana holdings. He figired the rebels would be just as open to corruption as was Batista, and would want the casinos to stay open because they brought in tourist dollars. By bringing the money, he was signaling to the about-to-be new regime that he was willing to make a big buy-in.