For MFI, they are designed for students who do not learn French between JK and grade 3. They teach most courses in French in grades 4, 5 and 6. Then, some courses are taught in English in grades 7 and 8.
Check the information from Ottawa public school board for the details.
MFI program:
http://www.ocdsb.edu.on.ca/documents/OCDSB_Publications/MFI.pdf
EFI, MFI, LFI, regular english and other programs information:
Ottawa Carleton District School Board | Our Programs | Elementary Programs
For MFI, Katimavik ES (Kanata) is a very good school in Ontario. (MFI school area: Katimavik, Kanata Lakes, Beaverbrook, ...etc.)
You can check whether you live in the school area at
Ottawa Carleton District School Board | Community Corner | Moving to Ottawa? | School Locator