I think I've mentioned this before but the Party of Regions (in blue here) was not a pro-annexation party. Elon Musk and others like to point to the popularity of the party in the Donbas and Crimea as a sign that they wanted to be part of Russia. However by the height of its popularity it had become much more of a big tent party.
On foreign policy, it mostly either was Euroskeptic or neutral. The only really visible pro-Russian position was on the status of Russian language. But by the 2012 parliamentary elections it had merged with some parties that were not very pro-Russian and the pro-Russian wing of the party was generally sidelined.
Of course with Maidan in 2014 we now know Yanukovych reneged on economic integration with the EU, but prior to that he had ostensibly promised EU integration.
So it is an oversimplification to say that Ukrainians that supported the Party of Regions wanted to join Russia. Polling reinforces this point. Prior to the Russian invasion when asked explicitly whether Ukraine and Russia should be one country, most people in eastern Ukraine said no.
It is correct to say that most people in the Donbas and Crimea spoke Russian and ethnic Russians were a significant minority population. But it'd be like assuming Americans wanted to join the United Kingdom. When these Ukrainians were asked how they identified, they identified generally as Ukrainian.