Hi there userfali,
it's vital that all your payroll forms be correctly filed to the government for the payroll of the previous year. QuickBooks Online Payroll is a great tool able to help you keep track of payroll totals so you know the amount for each form. I can provide some information about payroll forms.
When it comes to the T4 Summary, if you've used the .xml file generated by QuickBooks to submit your T4 forms to the government, the T4 summary is included in the .xml file. This information can also be seen in the section named Submit your employee's T4 summary to the CRA of this article.
All employees, including both active and inactive ones, should be shown in the dropdown when going to the Taxes tab, then Payroll tax. Select the Filing section, then click on the Year-end forms option.
if you have any other questions, feel free to reach out here.