Something along the lines of this...
void GetAllEntries() {
Leaderboards.YourLeaderboard.GetEntries(
isAscending: true,
callback: OnEntriesLoaded(is passed a list of "Entry")
errorCallback: OnError(is passed a string with error)
);
}
void OnEntriesLoaded(Entry[] entries) {
if (yourScore > entries[0]) {
LoadScene();
}
}
void OnError(string error) {
Debug.Log(error);
}