arachnaut's answer is probably the most definitive one you will get about Microft's support of the OS
How long Cakewalk will continue to make programs that will run under various versions of Windows, or to provide bug fixes..err I mean updates.. that will be backward compatible is more of a mystery. If your current version of Sonar runs under Windows 7, it should continue to do so. That does not guarantee that a bug fix designed to make the program work better in Windows 8 might not break that compatibility. In that case, you might have to uninstall the update and forgo the bug fix.
In any case, you can still get Windows 8 upgrades for $40.00, so if you install Win 7 now, you can save a cheap upgrade for later when the bugs are tamed a bit.