In that particular case I'd go with 'are'. Here are two examples from the Internet:
1) '
One percent of Canada's
population are long-term residents of health care institutions';
2) 'This is a generous community that should take pride in its philanthropy – in fact, if you did a tour of our city’s culture, medical and educational infrastructure, you would not believe that only
one percent of Canada’s
population was Jewish'.
In the first sentence, 'are' is used because the verb is followed by a
plural noun. I guess that's the way it works in such cases.