The youngster, who scored both goals in the Pirates' 2-1 win over Rochdale on Saturday, was originally on standby but has joined up with the squad for Friday's clash with Moldova.
Harrison has impressed Rovers fans with his performances in recent weeks and manager John Ward was singing his praises after his display on Saturday.
Ward said: "I had to ask my coaching staff the other day whether Ellis is left or right-footed because he strikes the ball so cleanly with both feet. He is a very exciting talent.
"There is a youthful enthusiasm about Ellis that you want to keep, while hoping he matures in other ways."
- Sports & Recreation