superstande: I actually got it working widescreen :) But not 1920x1080 - it's scaled, but at least it fills the whole screen.
So the bad news first - I'm afraid it may not (or may?) help those with different hardware.
But the Thing-To-Do™ was to go to Intel HD Graphics Control Panel (through rmb on desktop for example).
Going to Display and make sure scaling is ticked Scale Full Screen. Center Image, I ticked Override Application Settings.
That's that.
I remember getting some support from Gog to another game and they pointed me to the scaling option once.
Now, you need to know this will affect not just Anno 1503 but all applications, so use at your own discretion...
I'm thinking using Override only when playing this game.
WOW, now I can play 1503 and simcity 3000 on my laptop in fullscreen without black bars on the side ... Thanks a lot !!