Difference between variable using and statement using?

Im just wondering if there is any difference to using a

using

using

statement by doing this:

using var foo = new Bar();
foo.DoStuff();

using var foo = new Bar();
foo.DoStuff();

as opposed to doing

using (var foo = new Bar())
{
    foo.DoStuff();
}

using (var foo = new Bar())
{
    foo.DoStuff();
}