Starting May 2, 2022, foreign nationals who are citizens of the 40 Visa Waiver Program (VWP) countries will have to use the Electronic System for Travel Authorization (ESTA) to enter the United States at land ports of entry.
The paper Form I-94W, Nonimmigrant Visa Waiver Arrival/Departure Record, that is currently in use at the northern and southern borders is being eliminated.
The VWP allows citizens of the VWP countries to enter the United States for up to 90 days for tourism or as a business visitor without obtaining a visa. ESTA has been required for VWP travelers arriving by air or sea since 2008. Although Customs and Border Protection (CBP) officers have final say at the border, ESTA provides a kind of “pre-approval.” The new rule is simply an expansion of the program to “produce a consistent, modern Visa Waiver Program admission policy, strengthen national security through enhanced traveler vetting, expedite entry processing at land ports of entry, collect Form I-94W information electronically, and reduce inadmissible traveler inspections, generating time and cost savings for CBP  and Visa Waiver Program travelers.”
Except for one big difference, the ESTA regulations for land borders are the same as air and sea borders. VWP travelers arriving by air or sea must obtain ESTA approval prior to embarkation and provide the ESTA information to their air or sea carriers. VWP travelers arriving by land, often in private vehicles, will have to obtain the ESTA approval just prior to admission for presentation to CBP.
The Department of Homeland Security has a few tips:
The agency recommends applying for ESTA at least 72 hours in advance to avoid possible processing delays.
After May 2, 2022, any VWP travelers arriving without ESTA pre-approval will be asked to return to Canada or Mexico and make that application (which, hopefully, will take just a couple of hours, but that is not guaranteed).
ESTA is generally approved for two years and is valid for multiple entries. Anyone who already has a valid ESTA approval can use that and does not need to reapply for an arrival at a land port of entry.
Citizens of Canada are visa-exempt and have not been required to have an ESTA pre-approval for entry in visitor status by air or sea. This same exemption likely will apply for land entries.