It depends on what is the main contributing factor causing the squarish face. The factors could be :
a) wide bony face structure (needs bone shaving SURGERY)
b) big chewing muscles (needs Dysport or Xeomin
c) short, recessive chin (needs fillers or chin implants )
d) sagginess of fat tissues and skin causing jowls (can use Ulthera , Radiesse, Ellanse
e) chubby face ( Ulthera and / or Threadlift )
Therefore it all depends on your condition , so please look for a qualified doctor / plastic surgeon .