Best way to handle Switching of database connection in C#

String line = sr.ReadToEnd();

                        string connString = ValueCompair.Properties.Resources.ConnectionString.ToString();
                            //@"Server=MDT825;DataBase=Test;User Id=TestUser;Password=TestUser@123;Integrated Security=SSPI";

                        string query = line;

                        SqlConnection conn = new SqlConnection(connString);
                        SqlCommand cmd = new SqlCommand(query, conn);
                        conn.Open();