No, I think that the USA would have been a very powerful nation if the war had not happened because the factors that caused America being a superpower would have existed whether or not the war did. These factors could be its large population and landmass (US's landmass is far larger than Britain's, France's and Germany's combined). In addition, it was industrializing with this large landmass and population (unlike China which had both population and landmass but no industrialization).
You could also consider some more controversial factors such as a large intelligent Jewish population, slavery and cheap immigrant labour to produce cheaper goods and food, a less class-based economy for more efficiency and patriotic spirit that might cause Americans to work longer hours). However, some may disagree if these are factors. There are also many other factors that could be considered, which would still exist if world war two had never happened.
The USA would have these factors irrelevant of the war so would be a superpower irrelevant of the war. However, WW2 definitely helped them achieve their 'superpowership' faster by allowing them to sell weapons and profit from the war.
However, if you define a superpower as the most powerful nation (power as in military and economy and influence), then maybe Russia would have become more powerful nation than the US if WW2 did not happen, so the US would not be a superpower as it was not a powerful nation.
I think the USA would definitely still be a powerful nation if WW2 had not happened.