I don't see much chance of Belarus joining Russia. Belarus is all for it, or at least their government is, but my understanding is that the Russians don't care much for the Belorussians and see them as hicks.
Russians (of the non-liberal variety) generally see Belarusians as a part of the Russian nation which split off due to various unfortunate historical events (such as the collapse of the USSR, for example). According to an average stereotype of Belarusians in Russia, Belarusians work hard (unlike Russians), don't drink much alcohol (unlike Russians), and really love potatoes. In all other respects they're identical to Russians.
Lukashenko is also doing pretty well in his policy to eradicate Belarusian national identity in favour of a more Russified one. The eventual outcome would be unholy reunuion with Russia. One can see this in his attitude to the Belarusian language, Belarusian flags and so forth.
Actually, Lukashenko doesn't seem to be working to eradicate the Belarusian culture. He just doesn't care much about it.
Books in Belarusian language are being published, newspapers in Belarusian language are being printed, television programs in Belarusian language are being made, but few people actually read/listen to them, and Lukashenko doesn't want to actively promote them.
The old "white-red-white" flag is not officially banned. The use of it is somewhat discouraged because of its status as a symbol of the opposition, but it is not banned.
Also, about the eradication of Belarusian national identity:
Belarusian history textbooks and Soviet-era history textbooks are very different, for example, according to Soviet textbooks, during the times when Belarusian lands were part of the Grand Duchy of Lithuania, the Belarusian people were oppressed by Lithuanians and Poles, which tried to eradicate their national identity by various means (such as trying to convert then to Catholicism, for example). The Belarusian people struggled against the oppressors. When the territories of the former Polish-Lithuanian Commonwealth were divided between Russia, Prussia and Austria, Belarusians were actually liberated by Russia. The annexation of Belarusian lands by Russia during the partition of Poland is called "The Reunification of Belarus and Russia"
Today's Belarusian history textbooks don't state that Belarusians were oppressed and persecuted because of their national identity. The Roman Catholic Church did try to convert Belarusians, but it isn't described as a villainous plot, unlike in the Soviet textbooks. In fact, Belarusian textbooks state that the Grand Duchy of Lithuania's state language (before Polish and Latin were adopted) was Old Belarusian, the majority of its population (and nobility) was Belarusian, and its first capital was
Navahrudak. Before Lukashenko became president, the textbooks stated that Grand Duchy of Lithuania was the first Belarusian nation state, but that part was removed.
The actual levels of corruption in the government are low. It's really hard to tell whether Lukashenko himself is corrupt or not, though. Either he is not corrupt, or he is very good at hiding evidence.