The floating info boxes remain in place, they just float above the map, allowing the map to extend beyond the old boundary. But everything is statically placed, not movable, not a window to place in other monitor.
However, as would be expected, you can resize the games window to span multiple monitors.
My three monitors are pretty large in physical size, so the games default smallest text for 2560x1440 resolution is very easy to read, so I've been happy to keep on one monitor.
The only issue is the jump map, which is so small, but its the same as the previous versions. It is still helpful to move around quickly, but it is still very hard to see unit placements, too tiny. But everything else is so much improved that this does not hinder me in expressing my appreciation of this new game.