Singh will increase the number of NDP seats in S. Ontario. It is reasonable to suppose that his support will be newer Canadians, many of whom are Sikhs, Hindus and Muslims. How he fares in the rest of the country will depend less on his ethnicity and more on what is contained within the revised NDP platform.
Those old enough to remember how Bob Rae skewered the province of Ontario won't vote NDP, regardless of who is at the helm. Although there are many votes to be mined from Ontario, the NDP still has to get support from other provinces.
Winning the leadership race is one thing. Changing the minds of Canadian voters is another.