The question here is when does "Austria" join up with Germany.
Before the respective peace treaties? A WW1 POD that ends with a self-determination for germans (With some outlines: Polish sea connection, LoN Danzig, 1815 French German border, Industrial Silesia to new polish state) then Austria COULD look like this
http://en.wikipedia.org/wiki/Republic_of_German-Austria. But it would have to be some kind of earlier CP surrender (not very likey imo) and the Czechs, Slovenes and Italians wont be happy.
A post-versailles POD wherein Austria is allowed to join Germany by referendum with it's OTL borders, then "Sudetenland" becomes the focus point of german foreign policy post ww1 maybe South Tyrol too with antagonistic Mussolini.
Both these solution have the BIG problem of beeing unrealistic in a post WW1 world where Germany was to be weakend not strengthened.
The most realistic scenario, I can come up with right now, would be very close to OTL. (I think there are a number of TL's on this site where something like this happens)
Real rough: Weimar stable (No Nazis, better economics, more foreign concessions) => Austrian Civil War => Germany (part of LoN) intervenes to stabilize => Vote in favour of joining Germany.
After that maybe Sudetenland is up for debate (though Munich without Hitler is very unlikely).