Flying through Canadian airspace

I'll take a few flights between Rochester, NY and the Detroit area this
summer. Going through the Canadian airspace just seems so much
shorter. I can go IFR.

My questions is:

* I don't need to deal with customs at all, as long as I don't stop at
Canada, right?
* Do I need to use the ICAO flight plan for the IFR, or is the FAA
domestic flight plan sufficient for these flights?
* Since I'll use Canadian ATC service during the overflight, will I
get a bill from NavCanada when I get home?
* Is it easier to do this IFR or VFR? I assume doing this IFR would
make the Canadian overflight easier, but I'm very open to suggestions.

Thanks!