I would recommend visiting Youtube and searching for the Router Planer sled mentioned.
A power hand planer like the Bosch PL2632K is good for certain things, like doors, or using on the edges of boards, similar to a jointer, but more typically in a construction mode/setting. It would not be correct for flattening a top wider then its base, and I am pretty sure would leave marks, unless you did some sort of blade modification. (not recommended)
Where a router planer sled, is a slower method then a benchtop planer, but also cost effective way to learn and works on larger pieces then a benchtop planer could handle.
If you were to use a belt sander, to achieve what you want would take something like the Sandflee and lots of time and you might still need the router planer sled to take any twist out.