You can enter US as long as you have a "Valid Current Visa". Entry is
not permitted solely on the basis of I-94. I'm on H1 and travel almost
daily between Windsor and Detroit.
If you take your car you "MUST"
import the car, the officer would not allow you to enter Canada without
importing. If you want to avoid the import, your best bet is to take a
rental, tell the officer that you will drop off the car at an airport
etc.
As for getting back to US, you don't have to tell anybody, for
all you want you could drive straight back once all formalities are
done with immigration. Once your landing is done you could re-enter
Canada based on the landing permit even without a PR card but this can
only be done from US on a non commercial carrier.
Make sure you have
a current address in Canada before you start, you'll need this for the
PR card and SIN.