GERB actually aren't pro-Russian. They have always been pro-EU and Europe oriented and joining Shengen and the Eurozone happened in part because of them, though with a huge delay. They however have very well used the pro-EU stance to hide the rampant stealing of public funds and corruption surrounding their 10+ year ruling, which is the main reason people protested against them so many times. A bit Orban-esq they have also pretty much filled all institutions with their people, so it's hard to clean their mess.
Radev on the other hand has always been a pro-Russian proxy, though unlike Orban he is much more calculated with his words and actions. He is taking the "diplomatic" and "national" approach, though if you listen to his comments they are clearly favouring Russia.
Even though this guy was President for many years, that position is without much power here, so he hasn't had the chance to do much trouble. But he did manage to plant his seeds in many people's heads, as he always blamed whichever party was ruling for all the troubles in the country and many believe he is our new "saviour".
Compared to Hungary, the situation here is much more complex, as there isn't anyone as popular are Magyar and there are several strong parties, which always get practically the same number of votes.
Radev is surely winning, though the hopes are for the sane people to do damage control. But the truth is there aren't any many good choices, so it's going to be a lose-lose situation.
I don't expect a coalition to be formed, but it will depend on the number of parties passing the 4% threshold. So yeah, we are once again hitting the never-ending elections cycle, which the country has spun into since 2021.