Hello Joyce, I apologize for my late response. We transitioned from SAP HR and payroll to ADP in September 2021.
Functionality that we had with SAP and do not have anymore are:
-retro active pay
-and the ability to issue two T4 (under two different RP numbers) for same employee. We would need to terminate the employee and rehire to add a different EI-employer rate.

Please feel free to ask questions. I’ll answer if I can.