Obviously Campana is ahead defensively, an above average defensive center fielder vs an above average left fielder.
Campana also leads in average an on base percentage, but is behind in homers and slugging. wRC+ which is supposed to be something like an absolute value of runs created by offense (including steals) puts both hitters at 95, which is 5% worse than average.
The biggest difference between this year and last year (when he was decent) is that he walked 8.2% of plate appearances last year and only 4.9% this year, dropping his OBP from 322 to 285. Based on his later career there is still a chance of a semi-rebound and he still might be better than Campana. Because of the fielding difference, Soriano would have to outhit Campana by quite a bit to provide equal value.
My dream is that the Cubs will trade him to Floriday+ all the remaining salary to get Logan Morrison, who has angered his team.
In reality he will probably be a Cub next year. We'll just have to hope for a decent season.