@astral101 to make it fair compared to wage earners, 50% of the SE Tax ( SECA) is included as an adjustment for AGI computation ( Wage earners pay 50% of SECA, the employers pays the other 50% making FICA tax for wage earners 50% of SECA).
You claim the SECA immunity now but do go the SSA and show the certificate of participation and keep that with you for future ref. This is kind of back-door because your employer is in Canada withholding the equivalent of FICA/SECA.
But this work because those are the facts and circumstances.
