It wasn't possible for him to add you or declare you as his common law partner when he landed - that's not how it works. To add you as his common law partner, he would have had to have done this BEFORE landing in Canada and becoming a PR. He would have been required to return his COPR (landing visa) and let IRCC know he is now common law. He would have then been required to submit all of the paperwork to add you as his common law partner including PCCs, completing the medical and providing proof that you have lived together for a year. After taking additional time to process your information, IRCC would have then issued him a new COPR listing his status as common law (rather than single).
As far as he remembers,
-He declared me as his common-law partner when he filled the application form.
-However, he didn't have enough income history to get me PR. So, he didn't put me as an applicant for PR. So I was not considered as an applicant.
-When he landed, he asked to officer whether he can sponsor me later saying he has a girlfriend who has been living together for several years. And the officer said it will be okay.
This is everything my husband remembers....