Hmm. Detroit Approach controllers usually seem annoyed if you're
calling for anything but to cancel IFR. I supposed it's a workload
issue. I called to ask about routing once, and they advised me to file
direct and be ready to write when I called back for my clearance.

If you approach Detriot from the south, your routing anywhere north of
the city will be vectored to the west, around Willow Run, then to the
VOR, then on direct.