Operation Unthinkable (a British attack plan, requested by Churchill) was planned shortly before VE Day, and Plan Totality (an American attack plan, requested by Truman) was planned in August of 1945.

However, both Unthinkable and Totality were completely infeasible, the first due to the overwhelming Soviet superiority in Europe, the second due to the US not having nearly enough atomic bombs to carry out the attack.

An attack plan doesn't necessarily mean hostility (look at War Plan Red, an American attack plan against the British Commonwealth, for example), the Western Allied nations and the USSR weren't exactly the best of friends before the war, and it is unlikely that anyone considered the alliance a long term one. While not enemies, leaders of all nations involved realized that there would be some post-war tension about spheres of interest. For example, the issue of Poland came up at the Yalta conference, which was an issue since the German-Soviet partition of Poland, and certainly in the back of everyone's mind throughout the war. Another issue was the establishment of democratic governments in newly liberated Eastern Europe.