Hopefully someone with experience will help out, but here are a couple of links that may be useful.
This link contains the CIC questionnaire to establish kind of language proof you will need to provide:
http://www.cic.gc.ca/english/citizenship/language.asp
CELPIP General-LS and CELPIP General are the IELTS alternates on this CIC list of authorised third party test results:
http://www.cic.gc.ca/english/helpcentre/answer.asp?q=572&t=5