If you don't have the libusb filter installed for that device avarice won't be able to find it.
You probably already have the Windows libusb port installed (if not, you can get it at http://libusb-win32.sourceforge.net); go to its bin/< platform > path and run install-filter.exe; then select your JTAGICE3 device.
Notice that once you have done this, your JTAGICE3 won't be visible to Atmel Studio anymore, unless you uninstall the libusb filter (using the same utility). If you need to go back and forth between avArICE and Atmel Studio, you'll have to repeat this cycle over and over (sorry...)
Another problem is that JTAGICE3 is not supported at least until avarice 2.13 (which is the latest at the time I'm writing this). I had to download the head sources and build them in cygwin to be able to use it. the flag you're using (-mkII) is for another model and won't work because their USB IDs are different.