Unfortunately, there are serious consequences for not declaring a non-accompanying member of the family class in your scenario.
Page 11 (5.10 and 5.11) of the Overseas Processing Manual – Processing Members of the Family Class states the following:
Applicants must declare all family members when applying for a visa and must again declare all family members, whether accompanying or not, prior to obtaining permanent resident status. Permanent residents who did not declare all their family members on their application are reportable under A44(1) [see also “Sponsor who may be subject to an A44(1) report” (section 10.5 below) and “Misrepresentation” (section 5.22 below)]. In addition, all family members, whether accompanying or not, must be examined, unless the appropriate officer determines that they are not required by the Act or the former Act to examine the family member [R117(10)]. Family members who were not declared and examined are excluded from the family class and may not be sponsored at a later date as per R117(9)(d) unless R117(10) applies.
All family members, whether accompanying the principal applicant or not, are required to be examined unless an officer decides otherwise. Normally, an inadmissible family member, whether
accompanying or not, would render the principal applicant inadmissible.
For more information about the specifics of your situation, you can contact the CIC Call Centre (in Canada) at 1-888-242-2100.