Do you realise that if that was to happen there would be another world war bringing misery and deaths of thousands or millions of people?
Do you really know much about the history of these lands that you can so undoubtedly claim that a certain land belongs to a certain country.
Take Crimea - last year they were part of Ukraine but suddenly now they're Russian .... hmmm .... If you're American, imagine living in Texas and waking up as a citizen of Mexico one day. You may claim that the majority of people in Crimea are Russians but then you forget that Crimean Tatars were expelled from Crimea by Soviets in 1944 even though they had lived there since the 15th century. Should we return Crimean to Tatars? http://en.wikipedia.org/wiki/Crimean_Tatars
I'm Polish so I'm also quite interested in your suggestions concerning the borders of my country. As for Silesia, Pomerania and Prussia (region), I don't know why you state they are 'undoubtedly German' as all of these lands belonged to Poland longest in their history. They were occupied by Prussia (the state) from the 1790s to 1914 due to the partitions of Poland but they weren't Prussian. In fact, they were Polish before even the state of Germany was founded and rulers of Prussia were vasals to the Polish king.
http://en.wikipedia.org/wiki/Prussian_Homage
Prussia (region) was for some time inhabited by Germanic Teutonic Knights but they were also brought to the Polish lands by the Polish king Konrad Mazowiecki to spread Christianity - what they spread was terror and killing which resulted with the Polish-Lithuanian- Teutonic War won by the Polish_Lithuanian Commonwealth and the order was expelled from the lands.
For example, parts of Silesia used to belong to Bohemia as well (hmm, should we divide Silesia into three equal parts for Germany, Poland and the Czech Republic?
As for pre-war Polish lands, they were inhabited by Poles because of the territories of Poland in the times of the Polish-Lithuanian Commonwealth. Poles were expelled from these lands into Poland and Siberia by Soviet authorities and as much as I feel sorry for these people I don't want present day people of these lands to share the same fate - pack your stuff and get out of here, you don't belong here anymore ...
You say that Northern Bukovina used to belong to Czechoslovakia and Czechoslovakia doesn't exist anymore - should we give it back to the Czech Republic or Slovakia?
If your grandfather fought in WW2, ask him what he witnessed. Shifting borders brings death and misery of people, we don't want that. Moreover, many of the territories you talk about used to belong to different countries in its history so it's impossible to say which country deserves a certain land. Also, keep in mind that the population of these lands is far more homogenous than it actually was before WW2.
So for example 'returning' Silesia, Pomerania and Prussia to Germany would result in expelling Polish inhabititants (and interestingly enough that's what Nazis did in 1939 - 3 million Poles were made to left their homes for good without looking back)
http://en.wikipedia.org/wiki/Expulsion_of_Poles_by_Germany