*** Out of date info warning ***
But:
I (a UK national) flew a 172 from Canada to Reno and back in 2000 with the Visa waiver. The only problem was that you had to have the visa waiver prior to the flight. In my case this involved driving to the border post S of Boundary Bay, getting the visa waiver, doing a 180 in US territory and driving back to the plane to make the flight.
Now in the era of ESTA there are no more visa waiver forms. You apply online and get a confirmation number valid for two years. No more green I-94 form to fill in on the flight to the US (You still have to complete the customs form).
Is ESTA good for private flights? I don't know, but back in 2000 no-one in Pacific Flying Club knew about the visa waiver form either. That's how I came to be driving to the frontier post that morning! How did I find out? A simple phone call to US immigration at Bellingham Airport. I made the call because I didn't quite believe the information I was being given, just like the OP.
So why not call US immigration at your intended port of entry to the US and ask them? And if it's an N-reg flying into Canada, perhaps you should call the Canadians as well. Please don't forget insurance, mandatory in Canada. I doubt many US FBO's carry insurance for flight in Canada, and that's before you introduce the 'foreign national' part!
And then there's eApis....
Still if you can do it's worth all the hassles. Go for it.
A final thought: Are you sure you want a Visa in your passport? The queues at the US 'frontier' are long enough already with their new computerised system.