Read a few years ago on the Cooking Light forum that canned pumpkin is actually not pumpkin at all but rather butternut squash.
Since we always have a bumper crop of butternut and it over winters well I have a constant supply of it on hand. I use either interchangeably in recipes depending on what I have on hand and that includes making holiday pies with the butternut rather than pumpkin. You can also substitute sweet potato for either. Ann in TN