How can I change my iTunes Store to the USA, so my apps will update? Dialog says my account is not valid in the Canadian store, switch to US. But it won't let me do it.

My app updates in iPad won't install, when I hit update, it says my account is not valid in the Canadian store, and I must switch to the US store before purchasing. So, I sign out of Canadian store, and try to sign into US store, and that won't work either.

It says my Apple ID is not valid in the US store, but it must be, because that's where I made my purchases of all those apps in the first place.

Is it possible I am missing something here? Is this my fault? Can anybody offer a suggestion as to why I cannot sign into USA store?

Thanks for any and all help.