Entity Framework (Core) Query Multiple Tables From 2 Different Databases

How can I write a query to get data from 2 (or more) tables from different databases with EF Core? I have now the following code:

var items = (
    from o in _db1.Orders
    join c in _db2.Customers on o.CustomerId equals c.CustomerId
    where c.CustomerId = 1
    select c;
).ToList();

In MySql I have this query that needs to be transformed to the expression above (Linq).

SELECT c.* 
FROM db1.Customers c
   JOIN db2.Orders o ON c.CustomerId = o.CustomerId 
WHERE c.CustomerId = 1;

Please help