The incident came to light Monday in a release in which the force said six to eight of some 75 constables hoping to become sergeants and sergeants working to make the rank of staff sergeant were writing exams in April, The (St. Catharines) Standard reported.
Police Chief Wendy Southall told the Canadian Broadcasting Corp. an officer tipped the force off in May that some of the candidates had acquired the test and answers in advance.
Because the officers weren't charged, their names were not released, but all were eliminated from the process and given undisclosed disciplinary penalties, the CBC said.
However, all of them will be eligible to write the exam again next year, the reports said. The force said the exam process will be completely revamped before next year.
Meanwhile, police union spokesman Paul Di Simoni told The Standard the officers shouldn't be judged too harshly for the alleged misconduct.
"They're all excellent officers, but it's a situation which they found themselves in," he said.