根據CNN，從陸路加拿大和墨西哥回美國的已打疫苗公民不需要提供Covid 測試

Is testing required?

Fully vaccinated air travelers are still required to test negative for Covid-19 within three days of their flight's departure for the United States, in line with the current testing rule.

As mentioned above, unvaccinated American citizens will be required to take a Covid-19 test within one of day of their departing flight and again after arrival.

There is no testing requirement at land borders.