welcome - 환영해! but welcome back 돌아온걸 환영해! but it's a little bit awkward in Korean expression...um..not sure but for me. um... welcome back 다시오게 되신걸 환영합니다. we use this expression for customer or guest, not for friend. if you want to use it for your friend, i think 다시 보게 되어서 반가워! it's better. it means good to see you again.

1) Welcome back! 돌아온걸 환영합니다. 2) Welcome back to Canada. 캐나다로 돌아온걸 환영합니다.