Here's a few quick screen grabs of the A-PRO Control Surface Plugin, showing the Track, Synth, and Effects modes.
 
In Track mode, you can use the left/right arrow buttons to switch banks of 8 channel faders.  In my first pic, the green highlights the tracks that are being controlled.  The 9th fader controls the master.  The A1 & A2 pads let you select tracks by previous/next.  A5 & A6 mute and solo the selected track. And the transport buttons works just like the one in the Sonar GUI.
 
The labels under the rotary knobs and faders indicate their control assignment in any given mode.
 

 
When you open a synth plugin, it switches to synth mode and it will show the default parameter controls for that synth.
 

 
When you open an FX plugin, it switches to effects mode to show the default parameter controls for that plugin.  It seems to work OK with many of the newer Cakewalk plugins.
 

Does anyone who has the A-300 know how to bring up the A-Pro control surface plugin menu as shown in the screen shots above? I can't find anywhere in which I can bring that up, and I'm only able to control plugins with the a-pro, not my transport or faders. Any help will be much obliged.

PM abaca,, he's a super helpful forumite and seems he'll know for sure. 

The control surface plugin is a separate download and install from here:
https://www.roland.com/us/support/by_product/a-300pro/updates_drivers/
 
Just scroll down to the link for "A-PRO Series Control Surface Plug-in for SONAR"

The readme for the control surface setup is is the zip folder.
 

First off, thank you for taking the time to help me with this--very appreciated. The plugin had shown up under plugin manager under control surfaces, but I uninstalled and downloaded the plugin again. It still shows up under plugin manager in utilities but I can't find any way to open it. The read me file says the following: From SONAR’s menus, click [Tools] – [A-PRO-1]. I'm assuming this should be in utilities but there is no reference to an A-PRO 1 plugin anywhere. There is a generic ACT midi controller 1 that I can open in utilities but it brings up the generic MIDI map page. I still can't open the a-pro control surface plug.

Solved! I uninstalled and reinstalled the a-pro drivers as well as the plugin. When I configured the a-pro with the new drivers I was able to see a-pro under utilities for the first time. Now I can start to really use this thing for more than just the keyboard. Thanks again for the help!
 

cmj,
 
How's this working out for you?  A friend had a used A-300 he is going to sell for $180, and it interested me as I would like to have a controller in addition to the midi keyboard...The Console 1 looks nice, but its $499 and at this point only works with Softube and UAD plug-ins of which I have none...
Does the A-300 work with any 3rd party plug ins besides Cakewalk's??
Thx!

Just a heads up.
I was looking at controllers today and learned that not all controllers have standard size keys.
 
 

timidi
Just a heads up.
I was looking at controllers today and learned that not all controllers have standard size keys.
 

The A-300 is standard.