@kagemusha as I understand the totalization agreement between Canad and USA ---https://www.ssa.gov/international/Agreement_Pamphlets/documents/Canada.pdf
whether you are employed or self-employed while working in Canada / Quebec, only the local tax authority collects the equivalent FICA / SECA taxes. You do not have to file a schedule -SE for US tax purposes. The advice from the IRS agent ( long time ago is correct ).
You report your world wide income , for US tax purposes, as you have been doing in the past . No SECA or FICA requirement from the USA.
Hope this helps
pk
