I was wondering if it would be possible to arrange a longer stay (I have some travel plans that would take longer to complete: Appalachian trail, route 66, etc.) by first applying for B-2 visa to stay for 6 months, then briefly leaving US to e.g. Mexico or Canada and then applying for the Visa Waiver and returning for 90 more days?
So I was wondering if it's technically possible, and whether the authorities may question the situation and interview me? I'm an EU citizen. Thanks!
Technically you should not be admitted on the VWP if you have a valid B visa. And there's no reason why you should want to be: you could just as well spend six months in the USA on a B visa, then briefly leave to the US or Canada, and then be readmitted for six months on your B visa.
In fact, you can ask for up to one year at your initial admission. I suspect that it would be difficult in practice, but it is possible in theory.
You should also bear in mind that if you spend more than 183 days in the US, you're likely to trigger the substantial presence test, making you a resident alien under US tax law. You would then be liable under US law to report your worldwide income and figure your US income tax liability accordingly.
