I don't think I've ever driven on Cary Road, but I've driven on Marlbank Road which connects to it. According to this annotated map from the Globe and Mail
http://maps.google.ca/maps/ms?hl=en...,0.14986&t=h&z=13&iwloc=00047f1b1cc0a91a4c443 Jessica's body was found on Cary Road about a mile north of Marlbank Road with woods on both sides of the road. It's not a heavily populated area anyway, but this stretch of road looks very isolated. Depending on when Jessica was placed there, it may have been very low-risk -- late at night before she was found missing headlights would not likely have been seen or seen as suspicious.
That she was found along a road with trees may have meant tread or boot marks left in the snow would have been protected from sun-melt, which could have helped nail the perp. So, the isolated area helped keep the drop-off hidden, but that very same factor may have preserved the evidence needed to catch him... And it's been cold lately.