Can I start working for a new employer before my new work permit is approved?

Generally, no. If you hold a closed permit, you may only work for the employer named on it until a new permit is approved — starting early is unauthorized work and can damage your status and future applications. There are limited exceptions: open permit holders can change jobs freely, and IRCC has a process to request authorization to start with a new employer while a decision is pending. Always wait for written authorization before your first shift.