Don‘t quote me on this, however, members of the CF all undergo, at minimum, the "enhanced" clearance for security purposes, the same as any other Federal government worker.
Enhanced is simply a reliability check involving a CSIS check to see if you are a known terrorist, and ensuring your address and job history is complete with no gaps. There MAY be a credit check, to ensure no outstanding or recent bankruptcies.
"Secret" is the next level up, and involves a slightly lengthier check, of police databases, and for certain the credit check.
All I know about "top secret" is that most people don‘t have it, it takes a long time to get, and they are in fact, VERY thorough.
I believe "secret" clearance is mandatory for a comms course.
The exposure an "enhanced" level employee/soldier has to sensitive data is quite limited. The secret Tim Horton‘s coffee recipe is off limits, I‘m quite sure...
At most, you will handle information such as records regarding other employees/soldiers, such as training or attendance records, PRI/SN‘s, etc. ("protected a" and "b" stuff). You don‘t get into anything interesting or remotely risky until "secret" level.
I‘m sure an INT pers could correct me or fill in details.
I have only applied for Secret once, for an intelligence job with my civvi employer (customs), and since I didn‘t get the position, they didn‘t send the check in. I‘ve done that security check so many times it‘s ridiculous.