Thank you #Ponga and #canadianwomen for your generous help. I further clarified this issue with IRCC, who told me that they treat registered Indian as permanent resident in most cases. However when I read IRPR S.130. it says Sponsor must be Citizen or Permanent Resident, and does not mention Registered Indian at all, which confuses me...
http://laws-lois.justice.gc.ca/eng/regulations/sor-2002-227/page-27.html#h-79
Sponsor
130 (1) Subject to subsections (2) and (3), a sponsor, for the purpose of sponsoring a foreign national who makes an application for a permanent resident visa as a member of the family class or an application to remain in Canada as a member of the spouse or common-law partner in Canada class under subsection 13(1) of the Act, must be a Canadian citizen or permanent resident who
(a) is at least 18 years of age;
(b) resides in Canada; and
(c) has filed a sponsorship application in respect of a member of the family class or the spouse or common-law partner in Canada class in accordance with section 10.