on page 21 of the immigrant's guide (IMM 3999E) under dependents section :
Note: Remember that all questions in this section are about your dependant.
You can add up to five (5) dependants in this form.
To add a new dependant to the application, click the ―Add Dependant‖ button.
To remove a dependant from the application, click the ―Remove Dependant‖ button.
If you have more than five (5) family members, you must complete the Additional Dependants/Declaration (IMM 0008DEP) form for each additional family member in order to include everyone in your application.
Important
You must list all family members in your application for permanent residence, whether they are accompanying you to Canada or not. You must also provide details on family members whose location is unknown (including those missing or presumed dead). If you don't, you will not be able to sponsor family members at a later date if they are not listed on your application.
on page 4 of the immigrant's guide (IMM 3999E) :
If you are being sponsored as a member of the family class, your spouse or common-law partner (except where your spouse or common-law partner is the sponsor) must be included in your application as a family member. You must also include all your dependent children from your current and previous relationships, whether they will be going with you to Canada (accompanying family members) or not (non-accompanying family members).
All your family members, whether accompanying you or not, must be declared on your application and be examined. If family members are not examined, it is generally not possible to sponsor them at a later date. This includes children in the custody of a former spouse or common-law partner.
In addition, failure to declare family members on your application and have them examined goes against your duty to provide truthful and accurate information, and may cause you to be found inadmissible to Canada.
Also on the document checklist (IMM5491E) :
Original of Additional Dependants/Declaration(IMM0008DEP) completed by the sponsored person, if applicable.
I believe this should clarify the issue.
Good luck