"参加决赛的选手" can be translated into English as "the contestants/participants who have advanced to/reached the finals" or simply "the finalists".
"The contestants/participants who have advanced to/reached the finals" emphasizes the process of reaching the finals and is more detailed.
"The finalists" is a more concise and commonly used term, directly referring to those who are in the finals.
Both expressions are correct, and you can choose the one that best fits the context.