Security screening is defined as being three levels—reliability, secret and top secret—with an enhanced variant at each of those levels, for a total of six categories. Depending on the level of screening, different organizations get involved. Every single Government of Canada employee, co-op student, contractor and partner is screened to at least reliability status. I just listed off the requirements for what reliability screening entails. The one check that is done within the Government of Canada is to the RCMP criminal record database. Higher levels of screening would involve the RCMP again for a law enforcement record check. My RCMP colleagues can explain the difference, but a LERC, as it is known, is a much more exhaustive check. At the level of secret or higher, CSIS is also engaged to provide a security risk assessment.
Beyond that, as checks get higher and higher, it is largely the department that's making the decision and that's aggregating information together.