Name of a manga about angels and devils marriage for peace
What you're looking for seems to be a manhwa(Korean comics) and all of what you described seems to be listed:

cross dressing
she is watched over by two of the Four Guardians of Heaven
princess angel
unwanted marriage
Devils


Angel Diary (Manhwa)

Synopsis

The only Angel Princess of Heaven is betrothed to the Emperor of the Underworld. Unable to accept her future with the Demon King, she realizes that her only choice is to run away. Her plan is to join the human world disguised as a schoolboy! Now all of the Gods from Heaven and Hell are searching high and low on the earth trying to make sure that a wedding happens.
Source: MAL