What resolutions does WB3 supports? For me it's a deal breaker when a rts does not support widescreen and i have to play 1024x768 (Praetorians, Battle Realms, etc) and yes, i know, i know, old games where the engine wasn't ready to support bigger resolutions... So... does WB3 has 1366x768 resolution available?

Sorry no Battlecry for you. :(
The game never supported widescreen and there is no trick to my knowledge that unlocks real non stretched widescreen resolutions.
The game and his predecessors (WB2 still be the best title in the series) only support 4:3 resolutions with 1600*1200 res being the highest available. Still looks good on my native 1920*1200 display.
I'm using aspect ration method (I don't like the blurriness of stretch methods) for content displayed below my native resolution. The 150pixe; wide black bars left and right are barely noticeable.

Thanks for your answer, saved me 3$ since the game is on sale right now. :)

It's a shame, i can deal with the black bars on most games but on rts it's a no-no situation, i need full map awaress...

You have "full map awareness" as it's a 4:3 game.

That is an odd thing to say considering the game was designed with 4:3 aspect ratio in mind.
This is as if you would say you refuse to continue to live because you don't have the 350 degree vision of a horse. I need full round sight. 180 degrees fov of a human is a no-no situation. Harakiri