Hello mabbasi - in the application for sponsor they ask you explicitly if you are currently in Canada or Not, many applicants are not honest on this question, thinking CIC will not find out if you are in or ourside Canada. If a sponsor is living with their spouse in gulf, and apply for Family Sponsorship - CIC will be asking sponsor's intent/proof to move back to Canada once a visa is issued, and they will want to see all the documents during the phase of the application process or towards the end. This is something to keep in mind.
As part of your question " how will they complete background check " - in the applicants forms, they ask you where you have lived for more than 6 months in the last 10 years, based on that you will have to provide police clearance. Background check is two parts - criminality check and security clearance. Many agencies are involved for the clearance - A VO has there own communication process to reach out to the agencies to get a clearance.