Further thinking about this, reporting as other income may only apply if someone receives the Canadian benefits prior to receiving US SS benefits. However, these are retirement benefits and those reporting US retirement benefits get different treatment than ordinary income - SS taxable benefits are based on the various limitations and associated percentages that are taxable - basically the way SS benefits on line 6a reduce down to the taxable value on 6b would ignore the Canadian benefits if reported as you suggest as other ordinary income.
