With Soviet T1 it should be really easy to counter. Some Penals in scoutcar and kill them with flamer/ satchel. Keep making penals + scoutcar + sniper since ur opponent will not have manpower + ammo to deal with them because of the bunker spam. Oh and in this patch Guards seem to do sick damage to structures aswell
I dont recommend early ZiS since they are slow + expensive( in the big maps it takes super long to get there probably) and really nice warspoils for enemy
+1. You can also use mortar smoke on the bunker. When it is smoked you can walk past it.
If you do use a ZiS gun, remember that you can shoot into the fog of war by using Attack Ground. It is less accurate, but you can stay out of the bunker's range.