Your clients are not required to update certain information for FINTRAC within QuickBooks, dkoyataacct.
FINTRAC monitors transactions involving fund transfers. Since your clients use QuickBooks Online (QBO) Payroll only for recording and handle actual payments (paying employees and taxes) through other services, they may not have any reportable activities under the FINTRAC's mandate. They'll have to submit those details to their other payroll service provider where they have active money movements.
For more insight about QBO and FINTRAC, please see this article: What you need to know about FINTRAC.
Additionally, since your clients use QBO Payroll to generate paycheques, you may want to pull up payroll reports to maintain a clear view of their business's cash flow and ensure all financial transactions are accurate.
Let us know in the comments if there's anything else you need or concerns about updating FINTRAC. We're always ready to help you out.