For G36 latest (v1.2) rules regardless of 36 or 39 start it is the same. There is no ‘activating’ of units or rolling for units. Minors align with or are controlled by a major power. Table 4-4 Alignment Sphere of Influence (p.21) describes who and how:
Allies:
Nations Align with the Allies if the Axis declare war on them.
Nations come under Allied Control if they are Attacked by the Axis but the Attacking power is not at war with the Allies.
US gets all minor powers in the western hemisphere.
The British Commonwealth gets all the rest.
Axis:
Nations Align with the Axis if the Allies or USSR declare war on them.
Nations come under Axis Control if they are Attacked by the Allies or USSR but the Attacker (Allies or USSR) is not at war with the Axis.
Japan gets Siam and Mongolia***.
Germany gets all the rest.
Comintern:
Mongolia and Republican Spain (if they won) Align with the USSR if any other nation declares war on them.
These two come under USSR Control if they are Attacked by anyone but the USSR is not at war with the attacker.
***Not specified in the rules but the only option that makes historical sense.
In addition, there are Special Alignment Conditions for over a dozen countries that are outlined on p.22-23, but Greece and Yugoslavia are not among them. So