My friend from South Korea is visiting me in Canada. Is it possible for her to get an ESTA (Electronic System for Travel Authorization) while in Canada, and then visit the U.S. with me by driving across the border?
She can get an ESTA wherever she can find an internet connection, including in Canada, but she does not need ESTA to cross the land border. I have heard that it makes the crossing smoother, but I've never crossed the land border with a VWP traveler, so I do not know exactly how it works.
South Korea citizens generally do not require a visa to enter the US, and may enter under the Visa Waiver Program (this presumes she has no relevant criminal convictions/etc).
When entering by land an ESTA is NOT required. Instead she will be required to fill in an I-94W form at the border, be finger printed, and have her photo taken - which will entail a trip into the "secondary" area, although the entire process is really just a formality.
There is a US$6 charge for the I-94W.
To save a little time she can apply and pay for the I-94 in advance on the CBP Website, up to 7 days before crossing the border. She'll still need to go to "secondary" for the photo/fingerprints, but it'll be a little faster.