Don't worry, you're bound to get delicious results either way! Canned pumpkin is simply unsweetened pumpkin puree. The cans will most likely be labeled 100% pure pumpkin on the front, though ...
As long as your filling is already sweetened, you don't need to add any sugar. However, if you want to try the recipe with unsweetened pumpkin pureé, you'll want to add some sort of flavor enhancer.