There were quite a few people in high positions who were opposed to war against USSR
Erich Raeder as a head of the Kriegsmarine opposed war against the Soviet Union before the defeat of Great Britain. We could take this as a professional deformation, because at the time Britain was a great naval power and effectively blockaded Germany just like they did in WW1. In Raeder's professional opinion, in 1941 Germany should have executed the so called Mediterranean plan, and eliminate British presence in North Africa and Malta, capture Gibraltar etc... and then choke Britain out of the war by cutting off traffic of strategic materials to the island. Only after that war against the Soviet Union should be considered, especially since US started giving more and more help to British, therefore there was a limited window of opportunity to do this.
Hermann Göring as the head of Luftwaffe, was also "strongly opposed" to war vs the Soviet Union, again because his air force left an unfinished job with Britain, and because RAF now gradually grabbed air superiority over France and started night raids against Germany itself. He was not alone with this opinion in the Luftwaffe, generals like Erhard Milch and Otto Hoffmann von Waldau also doubted that the Soviet Union could be defeated completely before the onset of the dreaded Russian winter.
Joachim von Ribbentrop. although not a military leader, as a Foreign Minister of the Third Reich opposed the war vs Soviet Union. He may have had personal reasons as the Molotov–Ribbentrop Pact was a crown achievement of his career, and by his opinion gave Germany the chance to fight Britain "with both hands", chance that Hitler now squandered. It is said that Ribbentrop personally respected and even admired Stalin, so this could be another reason for his opposition against war.
Finally, it must be said that German army generals (Heer) wholeheartedly supported Hitler's ideas of conquest, including chief of staff Halder and field-marshals like Walther von Brauchitsch. This again could be professional deformation, because land conquest of Russia was a feat that none had achieved for centuries, and they felt themselves invincible after France. However, there were cooler heads even among them. One example would be Ernst August Köstring. Köstring served as a military attaché in Moscow, and argued that even capture of Moscow would not knock USSR out of the war, as Soviets had industrial capacities beyond Ural and could reorganize their transport network.