I have no idea what does security screening means? And what do you mean for
If the reviewers found something suspicious during security check, they initiate more comprehensive security assessment. It is carried out by the intelligence agency, CBSA and is associated with information from applicable foreign government, CIC can't control and can't accurately figure out how long it would take.
The funny thing is that you could be the subject for the security screening even though have not done anything. What I heard is the criteria are like your name, nationality, job, travel and residence history and etc. I guess if they found some meaningful similarities from database, they might check your information deeply.