PARIS, June 21 (Reuters) - Financial bookmakers expect leading European benchmark indexes to rise on Monday as investors bet China's vow to allow a flexible yuan exchange rate will boost sales of European companies in China. Financial spreadbetters expect Britain's FTSE 100 to open 44 to 47 points higher, or as much as 0.9 percent, Germany's DAX to open 41 to 44 points higher, or as much as 0.7 percent, and France's CAC-40 to open 35 to 37 points high