Public Shared Function GetResultsByKeywords(ByVal key1 As String, ByVal key2 As String, ByVal key3 As String, ByVal key4 As String) As DataTable
    Dim db As SqlDatabase = New SqlDatabase(Connection.GetConnectString())
    Dim dt As DataTable = New DataTable

    Using dr As IDataReader = db.ExecuteReader("sel_eHELP_ITEMS", key1, key2, key3, key4)
        dt.Load(dr)
    End Using

    Return dt
End Function

public class MyDAL
{
    private string _connectionString;

    public MyDAL(string connectionString)
    {
        _connectionString = connectionString;
    }

    public int MyDatabaseCall()
    {
        using (SqlConnection conn = new SqlConnection(_connectionString))
        {
            using (SqlCommand cmd = new SqlCommand("my sql", conn))
            {
                conn.Open();
                using (SqlDataReader reader = cmd.ExecuteReader())
                {
                    //...data access
                    return 0;
                }
            }
        }
    }
}

public class MyApp
{
    public static Dictionary<string, MyDAL> myDatabases = new Dictionary<string, MyDAL>();

    public string GetConnectionString(string database)
    {
        return System.Configuration.ConfigurationManager.ConnectionStrings[database].ConnectionString;
    }

    public void StartUp() // Global.asax Application_Start ?
    {
        myDatabases.Add("Database1", new MyDAL(GetConnectionString("Database1")));
        myDatabases.Add("Database2", new MyDAL(GetConnectionString("Database2")));
        myDatabases.Add("Database3", new MyDAL(GetConnectionString("Database3")));
    }

    public MyDAL DataAcccessLayer
    {
        get
        {
            string usersDB = FigureOutUsersDatabase();
            return myDatabases[usersDB];
        }
    }

    public void UseSomeData()
    {
        var myData = DataAcccessLayer.MyDatabaseCall();
        //Do Stuff
    }
}