My understanding is that for Mississauga office interview is at officer’s discretion: if you applied PR as provincial nominee or if you have completed post graduate degree in Canada , then an interview may be waived. For Scarborough office almost everyone gets an interview. However Scarborough office is certainly faster than Mississauga for oath after DM, typically 1 month vs 2.5-3 months for Mississauga so far. Maybe as covid cases decline significantly and Ontario opens up, they’ll speed up or even resume in person oaths.