Originally Posted by
sinanju
You can see the central parking walkway system that connects the two pretty easily on Google's satellite view. You'd leave B near where B38 is marked (though land-side, obviously), head to central parking, and then follow the signs to A:
http://goo.gl/maps/uyvdl
This would certainly work, but it would slightly faster to cross over to the US side and take that walkway, as mentioned by
lhl12.
The good news is that BOS-NYC flights have a lot of extra padding time. The bad news is that it is often not enough.