Question: What is the difference in the number of restaurants that passed and failed the canvass inspection type?
SQL: SELECT COUNT(CASE WHEN T2.results = 'Pass' THEN T1.license_no END) - COUNT(CASE WHEN T2.results = 'Fail' THEN T1.license_no END) AS diff FROM establishment AS T1 INNER JOIN inspection AS T2 ON T1.license_no = T2.license_no WHERE T2.inspection_type = 'Canvass' AND T1.facility_type = 'Restaurant'