That's the problem. This means you were common law when she landed in Canada and became a permanent resident. Since you were common law, she was obligated to add you to her application and declare you as her common law partner before landing in Canada and becoming a PR - and you were obligated to complete a medical, pass security and background checks, etc. Since she failed to do this, it unfortunately means she cannot sponsor you.
Regardless of how you respond to the fairness letter - your application is unfortunately going to be refused.
Having your wife sponsor you is unfortunately not an option for immigrating. You'll need to start looking into Canada's economic immigration programs (like Express Entry) to determine if you qualify to apply on your own based on your education / work experience / language capabilities, etc. You can find detailed information about these programs here:
https://www.canada.ca/en/immigration-refugees-citizenship/services/immigrate-canada.html
Good luck.