Has there ever been efforts by the German-part of Poland or the Czech to reintegrate into Germany?

I can only speak about the Czech part of your question. Strictly speaking, the answer is fairly simple – no, because there were no such regions to reintegrate.

I believe the issue might be somewhat different with Poland, as there fairly significant shifts and changes did indeed happen, but in case of the Czech Republic, its historical borders have remained largely the same for about ten centuries, with no parts "being Germany", so to speak, to lead to an effort like you mention.

Look at a map showing Europe around the eleventh century, this map of the Czech crown lands from 1747 or this one from the end of the 19th century. Of course, there have been additions to the Crown lands, such as Lusatia in the middle ages, or lands lost, like Silesia to Prussia during Habsburg rule, but the core lands of Bohemia and Moravia have stayed the same as they are in present day Czech Republic.

However, while historically or politically these lands have remained unchanged, there were attempts to divide them based on the issue of ethnicity, mostly centered around the two world wars.

Germans have lived in Czech lands since the 10th century, with local rulers actually inviting and encouraging them to settle the borderlands. This co-existence as "Czechs" or "Bohemians" regardless of language or origin began to change after the Habsburgs had taken over and with the rise of nationalism in Europe.

Under Habsburgs, the German minority would grow in power and influence, and major parts of Czech lands would be subjected to Germanization, and German culture and language became the norm for the upper classes. In the 19th century, there came a reaction in the form of the Czech National Revival, and a huge spike in the friction between the two peoples.

The Czechs clamored for a similar compromise as the Hungarians had managed in 1867, and in response there came the first notable attempt at dividing the country along national/language lines from local Germans who mostly opposed any attempts at anything resembling Czech independence. It was ultimately unsuccessful, but this sort of conflict permeated pre-war Czech-German relations and politics. Strangely enough, the situation was calmer in Moravia, where a compromise was reached in 1905 and calls for reform or threats of dividing the region were not as prominent.

The above culminated after the War, with the monarchy crumbling and Czechoslovakia declaring independence. The rump state of German Austria had originally claimed the right to self-determination as outlined by Woodrow Wilson's Fourteen Points and wanted to include the German speaking parts of Bohemia – the so called Deutschböhmen – but Czechoslovakia resisted any attempts at division and by late 1918 controlled its historical borders which were then confirmed in the 1919 Treaty of St. Germain.

The issue of areas with significant German populations trying to break away would arise again before the Second World War. Czechoslovakia had varied success in managing its multiple minorities, and it never reached a satisfactory solution. German-Czech relations were not completely destroyed with Germans retaining a presence in parliament and official use of their language, but they slowly deteriorated.

The fate of Sudetenland was the second major attempt – and in fact successful, if only for a while – of Germans trying to join Germany. At first, Konrad Henlein's Sudetendeutsche Partei did not call for outright independence from Czechoslovakia, instead prefering to improve its position from within. In fact, in the 1935 election it secured some 44 seats in the chamber of deputies, just one less than the biggest Czech party and seven seats ahead of the third placed social democrats, and 23 seats in the senate, tied with the agrarian party. Additionally, Germans in Sudetenland were not yet aligned with Adolf Hitler's regime.

However, by 1937 this changed completely as Hitler escalated his stance towards Czechoslovakia and the SdP became an extension of his will. Immense political pressure was soon joined by direct action, protests, even assassination attempts, paramilitary incursions and the like. Then in September 1938 the Munich agreement forced Czechoslovakia to cede Sudetenland to Germany.

During the war, the allied powers that originally took part in the Munich dictate declared it null and void, and acknowledged Czechoslovakia's pre-war borders. After the cessation of hostilities, Czechoslovakia like some other European nations forcibly expelled German nationals, except those crucial for industry, married to ethnic Czechs, or anti-fascists, and so this issue would not present itself again.

And that's pretty much it. The Czech Republic and its predecessors have not really had had any parts to which your question would apply, and what notable attempts of Germans trying to break away there were, those were fuelled by ethnicity and nationalism rather than historical or geographical ties to Germany.