I worked in Canada from 1990-1993. My earnings report shows no income for those years. Should those earnings be included in calculations for benefits? If so, what can I do about it? Or can I receive benefits from Canada for those years?
If you didn't pay U.S. Social Security taxes on your earnings in Canada, they won't show up on your Social Security earnings record. Nor will the Canadian earnings be used in calculating your U.S. Social Security benefits, at least assuming that you have enough U.S. Social Security credits to be insured (i.e. 40 quarters, or roughly 10 years of work).
I'm not an expert on the Canadian pension plans, but it sounds like you may qualify for some benefits based on your work there. The potential downside of that is that it would likely result in a reduction of your US Social Security retirement benefit rate. This is due to the Windfall Elimination Provision, or WEP (https://www.ssa.gov/pubs/EN-05-10045.pdf), that can result in a lower benefit rate for people who receive a pension based on work that was exempt from Social Security taxes. However, there is a WEP guarantee provision that limits the amount of reduction to no more than half of the amount of the non-covered pension, so it would still likely be advantageous for you to claim a Canadian pension if you qualify. For more information on the Canadian plans and how to apply for them, see the following reference: https://www.ssa.gov/international/Agreement_Pamphlets/canada.html.