What is your citizenship? If you are a US citizen with a valid US passport you are gold. If you are a Canadian citizen with a valid Canadian passport, you should probably bring with you proof that you own/maintain a residence on Canada (mortgage, lease, utility bills, etc) and proof that you can support yourself while you are in the US (bank account balances, credit card statements, etc). You may not be asked to present that information, but it's better to have it and not need it than need it and not have it.
Depends on your nationality and length of visit. It would be better to enquire with the US embassy or consulate before leaving.
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