Who must undergo a medical examination
You and all members of your family who are not already Canadian citizens or permanent residents, who are defined as members of the family class, must undergo and pass a medical examination, whether they will be joining you in Canada or not.  Members of the family class include:
                 •spouse
                 •common-law partner
                 •conjugal partner
                 •dependent children

Custody of a dependent child
All your dependent children must undergo a medical examination whether:
                •You have sole or joint custody, or
                •Custody is with the other parent
Note: If a child does not undergo a medical examination, you will not be able to sponsor them at a later date.

Spouse/common-law and conjugal partner, as well as dependent child, sponsorships require that the medical examination be completed before you submit your application, and proof of the exam be included with the initial submission.  Only examinations performed by a physician on Canada’s list of Designated Medical Practitioners (DMPs) will be recognized for immigration purposes.

Medicals

How to get an Immigration Medical Exam