public static ConnectionObject GetConnection()
{
	var connection = new SqlConnectionStringBuilder(ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString);

	var obj = new ConnectionObject
	{
		ConnectionString = connection.ConnectionString,
		DataSource = connection.DataSource,
		Database = connection.InitialCatalog,
		User = connection.UserID,
		Password = connection.Password,
		IntegratedSecurity = connection.IntegratedSecurity
	};

	return obj;
}

using(var rpt = new ReportDocument())
{
	rpt .Load(rptPath);

	var connectionObject = GetConnection();

	rpt.DataSourceConnections[0].SetConnection(connectionObject.DataSource, connectionObject.Database, connectionObject.User, connectionObject.Password);
	rpt.DataSourceConnections[0].IntegratedSecurity = connectionObject.IntegratedSecurity;

	crViewer.ReportSource = rpt;
}