http://www.cic.gc.ca/english/information/applications/guides/3900E2.asp
You cannot sponsor a person as your spouse, common-law partner or conjugal partner if
that person is under 16 years of age;
you are a permanent resident or a naturalized citizen of Canada and at the time you made your application for permanent residence, that person was a non-accompanying family member, former spouse or common-law partner and was not examined; or
you previously sponsored another spouse, a common-law partner or a conjugal partner and three years have not passed since that spouse, common-law partner or conjugal partner became a permanent resident.
You cannot sponsor a person as your spouse, common-law partner or conjugal partner if
that person is under 16 years of age;
you are a permanent resident or a naturalized citizen of Canada and at the time you made your application for permanent residence, that person was a non-accompanying family member, former spouse or common-law partner and was not examined; or
you previously sponsored another spouse, a common-law partner or a conjugal partner and three years have not passed since that spouse, common-law partner or conjugal partner became a permanent resident.