Wenn ich als deutscher Tourist nach Kanada gehe, kann ich die Grenze zu den USA überschreiten?

https://help.cbp.gov/s/article/Article-1258?language=en_US

You need an approved ESTA.

Effective October 1, 2022, all Visa Waiver Program (VWP) travelers intended to enter the United States by country will be required to obtain an approved Electronic System for Travel Authorization (ESTA) prior to application for admission at border ports of entry.

CBP encourages travelers to apply for a travel authorization at least 72 hours in advance of their occurring arrival at a U.S. land port of entry.

VWP travelers intended to travel to the United States by land, sea or air must receive a authorization prior to application for admission to the United States and continue to pay the $6 I-94W fee provided for in 8 CFR 103.7, unless entering within the 90-day admission period.

The I-94 can be filed for $6 through theCBP Onemobile application, which provides a more convenient way for travelers to apply for an I-94 up to seven days prior to arrival, review their past travel history, check their I-94 expiration date and obtain proof of their electronic I-94 from their mobile device. The application can be downloaded for free from the Apple App Store or Google Play. CBP requires travelers to obtain an approvedESTAand apply for the I-94 by using the CBP One or the CBP I-94websiteand avoid filling out the form I-94W at a port of entry.

You need a vaccination against Covid-19, too.