When I export 48k-24bit master mix and then go open that exported wav with a wave editor, the properties shown say "48000Hz 32 bit stereo" and "file format Windows PCM 24bit packed int (type 1(24bit))".   How can it be both 32bit and 24bit? 

It depends on where you are reading the properties. If the file has already opened in your wave editor (which one?) it is likely you are getting the properties of the wave in that editor, which may have padded out some bits to give itself some elbow room in processing. The file itself saved from Sonar to Windows storage as a wave file may have fewer bytes per sample.
 
If you want to know the bit depth of the file when it is saved to your hard drive that is a little more complitcated. Under windows XP it used to be pretty easy to get this information from a right click > properties>details tab in Windows Explorer, but MS in its infinite wisdom has decided that the only properties the user needs is the stuff you would use to tag and categorize your files. You can calculate the bit depth (not available under details) from the length, bitrate and file size, but the precision of these reported values (second, hundredth of a megabyte, and kilobit) are suboptimal for this purpose. You can use a hex editor to look at bytes 35 & 36 of the file to see how many bits per sample. There is a free utility that can do this for you if you find you need it often.
https://mediaarea.net/en/MediaInfo

It has been processed using 32 bit resolution (floating point) but as there is no hardware capable of playing anything more than 24 bit that's what you end up with.

32 bit and even 64 bit files can be created by software and exported and imported but when played, the hardware has to play it at 24 bit

Mind you this is a very simplistic explanation by a lay person.

There are a variety of places in Sonar where you can set at which rate files are imported, processed and exported.

The wave editor has converted your file to 32 bits for editing purposes, as suggested by slabartfast above. Most editors will subsequently save the file in its original format after editing, so no harm's done.
 
If you want to verify that it's really a 24-bit file, use some utility other than an editor or DAW such as Foobar2000. (Windows Explorer itself can also tell you, but not in a straightforward manner.)