1. since you are already divorced and you are the main applicant, your ex-wife's visa/landing paper is no longer valid. trying to enter canada using that landing paper is illegal and fraudulant.
2. best is to try contacting cic to apply for a change in family status. and see what they say. in this case you need to act quickly since your visa will expire in august.
3. remember that your ex-wife cannot land before you. if you don't hear from cic near august. you can try to land with your son at a date as late as possible, so to prevent your ex-wife to land in canada. but you have to tell the officer at the border that you are divorced. sorry to suggest in this way since it is bad for your ex-wife's life. but the fact is that you are divorced, so she is not entitled to the immigrant status anymore. it is illegal for you to assist her obtaining landed status.
2. best is to try contacting cic to apply for a change in family status. and see what they say. in this case you need to act quickly since your visa will expire in august.
3. remember that your ex-wife cannot land before you. if you don't hear from cic near august. you can try to land with your son at a date as late as possible, so to prevent your ex-wife to land in canada. but you have to tell the officer at the border that you are divorced. sorry to suggest in this way since it is bad for your ex-wife's life. but the fact is that you are divorced, so she is not entitled to the immigrant status anymore. it is illegal for you to assist her obtaining landed status.