収入要件とその免除については、スポンサーガイドのWho can sponsor?の項に記載があるので確認してください。
Who can sponsor?
You may be eligible to sponsor if: (中略)
・you have an income that is at least equal to the minimum necessary income, the amount of which is published yearly by the Canadian government.
This condition does not apply if you are sponsoring only
- your spouse, common-law or conjugal partner who has no dependent children, or
- your spouse, common-law or conjugal partner whose dependent children have no children of their own, or
- your dependent child who has no children of his or her own.
http://www.cic.gc.ca/english/applications/guides/3900E2.html#wp1015640