Can Summer Triangle asterism be used for navigation? I am wondering, whether is it possible to use vega-altair-deneb asterism for navigational purpose? Or if there is any geometric relationship of it with Polaris?

Any idea. 
Thanks
Yes, it can be used, but it is not easy.

For the latitude, you usually need to know the Alt of Polaris. You can derive that if you know the Alt of two of the three, but the (spherical geometry) formulas for that are not simple.

For the longitude, you need Greenwich time and the RA of any star. Any star includes Vega, Altair and Deneb ;)