So... Aero Snap is able to make programs like Guild Wars 2 fill the entire screen EXCEPT for the taskbar which is amazing. But I have to drag/drop it everytime I want to do it. It's not a big deal but it would be handy.

 

Is it possible to somehow make a window automatically Aero Snap itself when you open it?

There may be some super convoluted way to do it, but the short answer is no.

 

That said most games that boot windowed should have a resolution setting in their graphics which will dictate the size of the window - finding that and changing it to match your actual screen res would achieve a similar result.