I think you can preserve anything by canning if you do it right. The big difference is low acid v.s. high acid. Low acid foods have to be canned in a pressure canner for a long time to kill 'em all the way dead for sure or there is a risk of botulism which is deadly. You could can pumpkin pie filling but the eggs would cook and jell, so that wouldn't work too good as you want them cooking and jelling in your pie.

The question to ask is what's worth canning? It takes a lot of time and energy (your energy and some kind of energy to heat the stuff) to can, especially pressure cannning. You also have to buy lids and sometimes jars, both of which are way more expensive than they ought to be. Also, some foods don't taste that great canned. Meats are a good example, as are many low acid vegetables. Canning is not going to improve your soup or pie filling any. Freezing is a fantastic option if you can do it. I run mine on solar, so it's free in a way. Most properly frozen foods, if not kept too long, taste almost fresh. Maybe the best thing to do is to just eat more seasonally. You can have winter squash for much of the year to make your pies, because the squash can ripen as early as august and keep through spring. If you want a few pies off season, just toss a little cooked squash in the freezer. I'm just about to eat my last one. Wish I had grown more. I can as little as possible. Anything that freezes better or dries fine or that I can store in the garden in the ground I just do that instead. I still can whole tomatoes, tomatillo salsa, jams, and a few fruits- cherries, and sometimes pears.