You will need a "virtual MIDI cable" to connect Sundog to Reason (I use Reason 7 in this guide).
macOS: Please follow the guide here: http://feelyoursound.com/setup-midi-os-x/
Windows: Please follow the guide here: http://feelyoursound.com/setup-midi-windows/
Basically you set the MIDI Out of Sundog to the virtual MIDI cable, and the "External Control" settings of Reason to the virtual MIDI cable as well. Check the preferences in both programs.
See the example for Reason on macOS below: You can reach this dialog by clicking "Preferences -> Sync". Set the "External Control" Bus A to your virtual MIDI cable.
Please note: You mustn't change or add anything in the "Preferences -> Control Surfaces" dialog! The settings there are only meant for external MIDI keyboards etc that are connected directly to Reason.
Then you have to route the tracks of Sundog to Reason. Please take a look at this image:
Box 1: You have to click on the "Advanced MIDI" button of the Hardware Interface device in your rack.
Box 2: You can assign the different MIDI channels to different instruments now. I use Thor on Channel 1 and Malström on Channel 2 here.
Important: I highly recommend to set all instrument numbers inside Sundog to "Off" if you work with synth plug-ins! This way the plug-ins will always stay on the preset that you chose inside the DAW and not change their sounds from time to time.
Please make sure that you don't create a nasty feedback loop with your MIDI connections. Reason should not send MIDI notes back to Sundog! Otherwise it might happen that these notes will trigger Sundog to instantly send new notes to Reason as well, and the whole circle starts again.
If you want to use an external MIDI keyboard with your setup you should keep these things in mind:
1) Set Sundog's MIDI In to your external MIDI keyboard
2) Don't use your external MIDI keyboard as an input device in Reason
This is important, because if you use the keyboard in both Sundog and your DAW you will get multiple MIDI note events in your DAW as soon as you press a key. One time from the keyboard itself, the other time when Sundog sends its notes.
Sundog can send MIDI sync signals to Reason. In the preferences dialog above you can see that the "MIDI Clock Sync" input is set to the virtual MIDI cable as well. But you also have to do the following:
1. Click on "Options -> Sync -> MIDI Clock".
2. Now Reason should start and stop if you do that in Sundog.
I hope this small guide was useful! If you have further questions (or found an error) you can contact me here.