Security assessment is examining risks of espionage, terrorism, and subversion; human or international rights violations; and organized crime. The security check is firstly carried out by visa officers based on the information and documentation submitted by the applicant. If it looks fine, then they pass the security check.
But If they think that an applicant requires a more detailed investigation, the applicant’s file is referred to partners for security screening. The security screening is jointly carried out by Canada Border Services Agency (CBSA), Canadian Security Intelligence Service (CSIS) and Royal Canadian Mounted Police (RCMP).
In short, if an applicant is not caught by security screening, it usually takes 10-20 business days. However, if the security screening is required, it would take tons of time cuz different organizations are involved and the communication between them is not that efficient. It would take a few months or a year. CIC can't control the process and can't figure out how long it would take. All can do is just waiting.
I really hope not being selected for security screening.