Bulgaria was a satellite state of the USSR so it can be both Bulgarian and USSR ammo. Nearly all the surplus ammo on the Canadian market is from somewhere in the USSR from the cold war years.
Bulgaria also uses the Cyrillic alphabet, almost identical to the one used by Russia, so the cans having Cyrillic script doesn't tell you much.
Most of the arms and ammunition plants were established by the Soviet Union on near identical equipment and held to near identical standards. The Czechs held themselves to higher standards so their arms and ammo are known to be superior to other Soviet surplus and I've heard many good things about Polish surplus stuff too. After that the differences between Romanian, Bulgarian, Russian, Ukrainian, or other ex-members of the USSR/Soviet Union are fairly small.
