Sonnen's making a good move calling out Wandy. He's in a very tough position in his career but is picking a fight that is appealing to him for two reasons;
1. There's some beef there already, and legitimate or not, both fighters are big names and popular (in different ways) with fans.
2. Stylistically it makes a lot of sense for Sonnen to fight a guy with a wild boxing style, who is susceptible to being taken down against strong wrestlers (not that Wand has bad takedown defence though).