I've received a couple of additional opinions on this bird from two more expert Toronto Birders and neither of them came back with Yellow-rumped or Pine. One thought Blackburnian and the other thought Cape May - reasoning below. As Reuven pointed out, the yellow wash on this bird's breast is not right for Yellow-rumped (neither are the light coloured feet) so I apologize for the incorrect ID.
Here are the cases for each species from the other two birders I heard from:
Blackburnian - Streaking, yellowish breast, wide supercilium and triangular face patch
Cape May - Short, pointed bill, shortish pale supercilium, yellowish flush behind the ear-coverts and on the breast. Crisp dusky streaking along the breast sides and flanks and the bold white wing bars.
So we are undoubtedly dealing with a 'confusing fall warbler'. I will likely post this bird to a Facebook bird ID group to see if we can get a consensus and will post the findings here.