It's not that simple - a computer is not as efficient either. Computers have caused people to be detained at the border simply because their name/date of birth matches that of a criminal.
A computer can run checks electronically, but it still requires someone to enter that data in order for it to do the search, right? Also, site checks during a background check are not possible by computer. CSIS on the other hand can do the leg work - by the way, a lawyer once told me this agency is capable of going right to your parents' home if need be.
Remember the gov't is making changes as a result of fraudulent applicants not to make yours or my life difficult. They can't win - one minute we are so worried about the invasion/loss of privacy, the next we want an integrated system. That is CSIS, CRA, CIC, HRDSC, etc as one. I named these ones because applicants require documents from each of these agencies for an immigration application.
Do we realise what we would be potentially giving up if we want that to happen? As it is, these agencies can not disclose information to one another about us without our consent. Integrating them may mean, you consent to one and you may have consented to the others as well and let the intrusion begin. No thanks.
Furthermore, I can't see how CSIS will fit into this integration? It's the one agency where an access to information request could come back with all information redacted except perhaps the date.
Everything is classified.
Try watching Border Security: Canada to get an idea of how they go about their work and just how much authority/power they have. It is a different experience watching it than going through it. They can search your belongings and your person without a warrant but the police/RCMP need a warrant for that.