sanyer

Moldova seems to be the most probable target of a Russian invasion. Factors that make this more likely:

• Transnistria is very much controlled by Russia, and has 1,500 "peacekeepers" that it could use. I can imagine an attack from Transnistria towards Moldova with significant support from Russia.
• Russia could try to annex Transnistria with Transnistrian government approving but Moldova trying to prevent that. I can totally imagine this happening
• Soft resolution criteria as pointed out by @DimaKlenchin 
• Russia is waging hybrid warfare towards Moldova more than in basically any places. This will probably intensify due to the Moldovan presidential election and a referendum about joining the EU later this year.
• Russian leaders are saying very similar things about Moldova now as they said about Ukraine before attacking it (Newsweek)

Factors that make Russian invasion to Moldova less likely:

• There doesn't seem to be enough troops in Transnistria for Russia to attack Moldova properly from there directly, and there doesn't seem to be any easy way to increase that number.
• Therefore, an invasion seems quite unlikely to happen without Ukraine collapsing, since that would allow Russian troops to enter Moldova. However, this doesn't seem very likely to happen in two years (~5%?)
• After Ukraine collapsing, it would take some time for Russia to start yet another war, so it seems like such an attack would happen outside the 3-year time frame of this question.

It is also conceivable that Russia would invade Georgia. However, it seems that the relations between Russia and Georgia are surprisingly stable despite Russia controlling over 20% of Georgia's territory. 

I don't see the invasion of Armenia or Kazakhstan anywhere in horizon, despite Armenia's ties with Russia deteriorating.