According to the CDC on 2021-01-24, the requirement that air travelers to the US have a COVID test before arriving does not apply to land travelers.
On January 12, 2021, CDC issued an Order requiring all air passengers arriving to the US from a foreign country to get tested no more than 3 days before their flight departs and to present the negative result or documentation of having recovered from COVID-19 to the airline before boarding the flight. Air passengers will also be required to confirm that the information they present is true in the form of an attestation.
Does this Order apply to land border crossings?
No, the requirements of this Order only apply to air travel into the US.
Note, however, that you may be subject to quarantine restrictions upon your arrival, and that these restrictions may be less stringent depending on whether you have been tested recently before arrival. These restrictions vary at the state level, so this issue can't be addressed without knowing your final destination in the US. I recommend searching for "[state] travelers COVID quarantine" to find further information. (Or you could edit your question, and/or ask another question on this site.)