Is an ESTA visa required when crossing the Canada border?

If you fly to the United States and you are eligible to apply for an ESTA, this is often the best option. However, if you are crossing the border from Canada or Mexico, you will not require an ESTA visa. The ESTA is only required if you arrive by air or cruise ship.

To find out if you need to apply for ESTA visit https://www.official-esta.com/

So what happens if I cross the border by land?

If you cross the border by land for the same trip that you would have made using an ESTA if you were arriving by air or cruise ship, you will be required to fill in the form I-94W. This is a form that you fill in at the crossing point
Form I-94W is only used if you are travelling for the same purposes as the ESTA visa. If you plan to work or carry out another activity, you will still need the correct visa

Find out more about the I-94-W at http://www.cbp.gov/travel/internation...

When leaving, make sure your departure is registered!

If you enter the USA on the I-94 or I-94W, you must make sure that the stub of the form is handed back to the authorities upon your departure, which should happen automatically. The stub is the part of the form that is attached to your passport and provides information about your trip.
If this is not removed, your departure may not be registered correctly. This could then cause problems when you next want to reenter the country at a later date.
If this happens and you depart by air or cruise ship, it’s not usually a problem because your departure from the country can still be verified. However, you should still keep hold of your boarding pass just in case for the next time you want to enter the USA.
If you leave by land and the authorities forget to remove the stub, this is more problematic - Along with your stub, you should also send documentation that proves you left the country, like a boarding pass.
If you no longer have the stub to send, you will need to file a Travellers Redress Inquiry Program (TRIP) request via the homeland security website.

To start your online ESTA application go to https://www.official-esta.com/apply/