Belarus has really been a positive surprise, not only because of the good results, but their style too. Usually teams of that level just clog up the neutral zone and hope for a miracle. Belarus, even though they are defensive, tries to build their own offence and will play when given the chance. Everyone who's been following the tournament (and/or previous years) knows how good Mezin is, and outside of the Kostitsyn-Grabovsky-Skabelka line that everyone mentions, they actually get some secondary scoring from the likes of Zadelenov (on first PP unit), Antonenko, Dudik and Meleshko.
Finland, however, has better depth overall and a better defense, which maybe tells more about the Belarussian d-men than the Finnish. Finland will have to apply their normal team defense and be able to pressurize the BLR defense, optimally by turning the game quickly from defense to offense. If they underestimate Belarus, they'll be screwed, especially without Niittymaki. This Belarussian team has shown that it is no laughingstock.
The outcome is difficult to guess here. Finland is, however, the favorite and if they can score early, a blowout is not out of the question. If Belarus and Mezin can hold the fort long enough, though, they'll get their chances: Belarus has a good powerplay while Finland is prone to penalty trouble. If that's the case, the game will be decided by one or two goals, and may require a shootout. That should be easy for Finland, as they have many players, led by Jussi Jokinen, who were good in shootouts this past season in the NHL, while I believe many Belarussians play in leagues that have not adopted the shootout.
Still, maybe the most probable outcome is one in which Finland plays their team defence while capitalizing on the weaker lower lines of Belarus. That way, we'll see a low-scoring game where Belarus scores a maximum of one goal and Finland gets 3-4. That is probably the type of game that Finland will be looking for, while Belarus hopes to play their game and wait patiently for those PP chances.