Crossing for visitors with a B1 and B2 tourist visa to the United States is still restricted. There is no crossing restriction for US citizens or residents. Passengers for a trip considered essential may also cross. For more information see https://www.dhs.gov/coronavirus/overview-dhs-response and the Official Notice of Temporary Travel Restrictions prior to your trip.
For tourists I'm not sure
Yes it is
Not yet
Only for citizens and residents, not with a visa.
And
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