I like to work with two video monitors where in the first I see the track view and the other I edit MIDI in the Piano Roll View.
When I double-click a clip in the track view, it opens the PRV, but I always have to maximize it manually.
Is there any way to open the PRV always maximized when double clicking a clip?

I don't know but you can use screen sets to expedite this. Plus if you are working with Windows 10 double clicking on the title bar will maximize it. You can also move the window to the top of the monitor and it should dock there. 

John
I don't know but you can use screen sets to expedite this. Plus if you are working with Windows 10 double clicking on the title bar will maximize it. You can also move the window to the top of the monitor and it should dock there. 

Thank you, but the problem is, even with ScreenSet and PRV already maximized, if I double click on another clip, PRV will get back not maximized. As I use dozens of instruments, this process of opening and maximize PRV every time, it becomes something boring.

I created this script with Autohotkey, I think it solved the problem (works also when pressing Alt+3):
 

SetTitleMatchMode RegEx
#IfWinActive, ahk_exe i)SONAR.*exe

~LButton::
 If (A_TimeSincePriorHotkey<400) and (A_TimeSincePriorHotkey<>-1) 
  Gosub maxprv
 Return

~!3::
maxprv:
 sleep 200
 WinGetTitle, Title, A
 IfInString Title, Piano Roll
  Send #{Up}
 Return
#IfWinActive