Okay, so here is the reason why it might not be required:
Apostille convention (the apparent reason why that indicator is there in certificate) is not specific to India. In that case, CIC would have explicitly mentioned that the marriage certificates needs to be attested by MEA/relevant authorities. Instead, they say "If the applicant married outside Canada, a copy of a legal certificate issued by the country, the territory or the region where the marriage took place must be provided." They never mention that the document needs to be validated for use within the Canadian jurisdiction (which is the entire point of the apostille).
So I have a feeling that it should be okay, even if it is not MEA attested. But again, this might be me reading between the lines to get convinced that I did the right thing.