It is impossible to look beyond Nadal for this final, there are just too many factors in his favour. He has never lost to Thiem at Roland Garros in three meetings and has never lost to Thiem in a five set match.
Nadal knows exactly what it takes to win the French Open where as Thiem is still searching for the first Grand Slam win of his career. In addition, Nadal had his feet up on Saturday while Thiem was battling Djokovic in the semi-final.
It all adds up to a comfortable win for Nadal at 11/10 in three sets. However, Thiem could start strongly and possibly take the first set into a tie break and Nadal is 11/2 to win the first set 7-6. After that, expect to see Nadal use his experience and extra day of rest to pull away and win his twelfth French Open title.