chan_beagle follows the so-far consistent device specification
methodology (Asterisk CLI command) of <device-type> active <device-name>

for chan_beagle, and your chan_beagle device named 'beagle1234'
it would be:

beagle active beagle1234

for chan_simpleusb, and your chan_simpleusb device named 'fred42'
it would be:

susb active fred42

for chan_usbradio, and your chan_usbradio device name 'usb5678'
it would be:

radio active usb5678

[since chan_usbradio did this first, I think you can see the reasoning
by which the particular syntax was chosen :-) ]

Also, you can do <device-type> active
(with no device specified) to see which is currently "active" (selected).

JIM WB6NIL