By Morgan Lowrie THE CANADIAN PRESS MONTREAL- Eighteen-year-old Hunter Sousa from Maine celebrated his high school graduation by hopping in a truck and heading to Nova Scotia to fight the biggest forest fire in the province’s history. Sousa works for the Maine forest service as an on-call firefighter, but had never before fought a fire. The call from his superior came on a Thursday. “They said they’d be meeting in Bangor Friday night and I had my graduation Friday night, so I graduated and got my diploma, and headed to Bangor and met with the rest of the crew, and then we headed to Nova Scotia,” he said in a recent interview. Sousa is one of the many foreign firefighters who were pressed into service as Canada battles its worst…