Flying through Canadian airspace

M wrote:
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.

I did this a couple of years ago.

* I don't need to deal with customs at all, as long as I don't stop at
Canada, right?

No customs.

* Do I need to use the ICAO flight plan for the IFR, or is the FAA
domestic flight plan sufficient for these flights?

Domestic flight plan worked for me (through FSS, didn't try duats).

* Since I'll use Canadian ATC service during the overflight, will I
get a bill from NavCanada when I get home?

Don't know this one, as I was flying a friend's plane and NavCanada
changed how they do user fees since then, I think.

* 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.

IFR made it transparent. Don't know about VFR, you'd need to go
through the rigamarole of a DVFR flight plan on the way back into the
US or something?