Loc: Maine (IBS-A stable since July '05!)
Insoluble fiber is insoluble fiber, period. It doesn't matter if you cook it, mash it, etc, it's still insoluble fiber. I don't think the amount of fiber in something decreases when you cook/mash it - I think it just breaks down a little so it's easier to digest.
What DOES drastically reduce the fiber in something is peeling it, so if you're not eating the skin, you're probably getting about the same amount of fiber as you would from canned.
(I've done a lot of home canning, btw. The process of canning is essentially cooking the fruit... so if you're eating it straight out of a can, or if you're peeling it and then cooking it yourself, it's essentially the same thing. The biggest difference is sugar content, but if you buy juice-packed fruit, you minimize that as well. Mind you, fresh fruit in season definitely TASTES better than stuff out of a can, but nutritionally, it shouldn't be all that different if you're essentially "processing" it the same way.)