I checked the canned pumpkin supply when I was in A&G this afternoon for other reasons. They had a fair amount on the shelf, certainly more than a case, priced at $1.79/can. Best used by date was in the spring of 2011. We have a couple of cans in the basement purchased last autumn with similar best used by date, so I am guessing that the stuff at A&G is from the 2008 crop but possibly 2007. As wendy noted, the use by dates are pretty far in the future relative to canning date.
I think that cooking up a sugar or pie pumpkin (two names for same thing) gives better flavor than using canned pumpkin. Moisture content will be higher for the fresh pumpkin than canned, so recipes may need tweaking human applications. My experience is that the various color forms of Hubbard squash produce a bit dryer flesh than pumpkin, more comparable to canned pumpkin, with superior flavor. Mashed, cooked pumpkin and winter squash freeze well. The larger, more ornamental pumpkins tend to be a bit stringy and more watery. I doubt that this would make much difference to a dog. Horses and squirrels love these pumpkins raw. Historically, the larger New England pumpkins were grown to feed cattle and horses in the early part of winter.