You can sign up here for a chance to be in the Cossacks 3 beta, which will feature several waves of testing, presumably to iron out as many bugs as possible.
In an earlier post on the Facebook page, GSC reveals the reason for this extensive beta test.
“These last few months have been extremely difficult for the team. We have been rushing around trying to get everything ready for the release date of the game. But as we all know, rush is a very bad companion in game development. So we decided to postpone Cossacks 3 release in order to hold a comprehensive beta-test of the game.
“We are preparing to start gathering beta-testers’ applications and assign the first wave of testers. With their help we are going to improve the game’s quality, test innovations and implement feedback from Cossacks veterans and newcomers.”