French Guiana is indeed a French region and not an independent state in its own right. It is, however, often referred to as a 'country' as the word does not necessarily imply independence. But yeah, to be precise, the country bordering Brazil would be France. So plain old France could be an accepted answer here, but I think 'French Guiana' ought to be retained as well so as not to mystify quiz-takers.
You are a bad quizmaker. One thing is to have errors. Another is to leave them there for 8 years. Simply astonishing to think you have a featured quiz, with other quizzes as low quality as this.
Alos, Colombia is spelt wrong.