I am entering the United States aboard a private plane, can I travel visa free?
If you are entering the United States aboard a private aircraft of a U.S. corporation that has entered into an agreement with the Department of Homeland Security to carry passengers under the Visa Waiver Program, you will not require a visa, if you are otherwise qualified to travel visa free. If you are entering aboard any other private or official aircraft, you will require a visa.
Taken from
Embassy of the United States London, UK - Visa Faqs
Can I enter the United States by land from Canada or Mexico under the Visa Waiver Program?
Yes. If you enter by land there is no requirement that you be in possession of a round trip or onward ticket. The immigration authorities at the border crossing will issue you with the arrival/departure record card, I-94W. You will be charged a $6.00 administrative fee; the fee is payable in U.S. dollars only.
Looks like you will need a B1/B2...
Don't forget about eAPIS...... and look at this
U.S. Customs and Border Protection - Travel
Mutt