By Andrea Shalal, Mike Stone and John TilakWASHINGTON/NEW YORK/TORONTO (Reuters) - Canada's Bombardier Inc is exploring the sale of a stake in any of its business areas, not just its rail unit, to ensure it can finish development of its delayed CSeries jet, according to four sources familiar with the situation.The Montreal-based company has hired investment bankers to look at a variety of financing options, the sources said, including selling aerospace or rail assets in full or in part, forming joint ventures or bringing in private equity investors.One source familiar with the company's thinking said Bombardier hoped to secure...