Yes, you can use Reason with Sonar because both support Rewire. Here is a tutorial that should help.
http://www.cakewalk.com/Tips/April03_AndertonPt4-reason.asp

I have used FL Studio and storm 2 as a rewire with no problems. I haven't played around enough with Reason to give a personal opinion, but their synths are usually seem well regarded.

There are certainly other emulations that will come close if not exactly match the Reason synths, but you if your happy with Reason, you won't need them as you should be able to work fine with Sonar 4 and Reason in the rewire environment.

Regards,

AJ

[This message has been edited by Bluezplayer (edited 05-17-2005).]