Open Sonar 7 and select "ReWire Device" from the "Insert" tab. According to Propellerhead, the manufacturer of the Reason and ReWire applications, ReWire acts as an "invisible audio cable that connects two computer programs."
Click on "Reason" in the ReWire menu. Review the settings on the pop-up menu that comes up. For most productions, you should leave these settings in their default positions. If you are planning on using a tool other than Reason to input MIDI data, select it as an input on this menu.
Select "Reason" from the "Synth Rack" pop-up menu that appears. A box will appear in the left-hand column of Sonar 7. Use this box to adjust any audio settings, such as a preference for mono or stereo.
Open Reason's main display window. Click on "Create" and click on a synthesizer. Highlight the synthesizer in the sequencer window, then return to the Sonar display. Connect your MIDI keyboard to the computer and press a keys to test the ReWire connection. If the ReWire connection is working, the Reason synthesizer will play through Sonar 7.
Click on the MIDI channel that you want ReWire to use for recording. Match the Sonar "input" MIDI channel to the Reason "output" MIDI channel.
Press the "R" button in the left-hand column to arm the track for recording. Play the keyboard; the sounds from Reason will now be recorded directly into Sonar 7.