The abbreviated version of the game was invented at the Greenyards and as well as the three travelling to the borders, four Warriors are also representing their country at the sport at the Commonwealth Games in Australia this weekend.
Vunisa will turn out for Marr alngside Academy scrum-half Kaleen Baretto.
Glasgow Warriors have twice won the tournament, entering teams in 2014 and 2015. Harlequins are the current reigning champions.
This year's invitational teams include Poland, USA Tigers and Crusaders.