According to the CRA guidelines for Non-Residents, you should only report on your Canadian Tax Return the income from your US Social Security for the part of the tax year that you were a resident of Canada.
What income do you have to report?
Part of the tax year that you WERE a resident of Canada
Report your world income (income from all sources, both inside and outside Canada) on your Canadian tax return.
Part of the tax year that you WERE NOT a resident of Canada