It would not be ethical or legal to spy on a country using a high-altitude balloon. Additionally, it is unlikely to be practical as high-altitude balloons are not equipped with sophisticated surveillance technology. The use of such technology to spy on another country would be considered a breach of international law and could result in diplomatic consequences.
Even if a high-altitude balloon was equipped with sophisticated spy technology, it would still be illegal and unethical to use it to spy on another country. The use of such technology without the consent of the country being monitored would violate their sovereignty and could have serious diplomatic consequences. Additionally, it could harm international relations and potentially lead to conflict.