Originally Posted by MSPeconomist

The contemplated purchase for the positioning flight would be LGA-YYZ operated by Westjet but sold as a DL codeshare. I assume it would leave from a different area of LGA from the terminals DL use, probably the central terminal, so that if there's an obvious delay, there would be no opportunity for the OP's two tickets to be changed to LGA-DTW-PVG, all on DL of course.