Apparently QBO Canada will set it up for you and handle the deduction, but you will have to make the payment.

https://community.intuit.com/articles/1431595-garnishments

I think you contact Canadian support here:

https://community.intuit.com/articles/1169453

Resolution for 'Canadian support issue: 'How do you set up a Garnishment in QuickBooks and then pay the amount to the CRA? Any advice you could provide would be helpful. Thank you.' available: Yes.

The Canadian support issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the Canadian support issue yourself by looking for a resolution described in the article. If it is a complex Canadian support issue or you are unable to solve the issue, you may contact us by clicking here or by using other Canadian support support options.

For more information about resolving issues related to Canadian support in Quickbooks/QBO or to get support for the issue 'How do you set up a Garnishment in QuickBooks and then pay the amount to the CRA? Any advice you could provide would be helpful. Thank you.', click the link below: