The easiest way would probably be to copy the "World of Warcraft" folder in your Windows Program Files folder to your Crossover bottle's Program Files folder. Then when you run the Crossover installer, tell it to "install" from the "WoW.exe" file in the folder that you just copied and then continue (this is mainly to help crossover set up the icons and stuff for you) and you should be good to go. WoW should show up in the Unity interface under the appropriate category.
On a side note, the above kinda uses alot of extra space on your hard drive, since it leaves you with two WoW installations. If you prefer to have both Windows and Linux share a single installation, that can certainly be done, too. The best way to do this that I know of is to use a symbolic link, which will basically point to the existing WoW files instead of copying them over (using much less space). I don't know how your computer is set up, so I'm afraid I can't give a specific example on how to do it, but the general way would be ln -s /path/to/Windows/drive/Program\ Files/World\ of\ Warcraft /home/(username)/.cxoffice/(WoW_bottle)/drive_c/Program\ Files/
in a Linux terminal. Please substitute your username and the name of the WoW bottle in for the items in parenthesis (and the real path to your Windows files, of course . 😉 ). Then, as above, run the Crossover installer and point it to WoW.exe to set up the icons and you should be good to go.
Hibba