Commission Junction is a network of advertisers and publishers. Publisher can choose and put links (text / banner etc.) on their site(s) and earn commission on sales/leads etc.
Commission Junction is an affiliate networks, through which merchant manage their affiliate programs and affiliate choose program according to their taste.
You mean both the advertiser and the publisher can choose what they like - like advertiser choosing in which websites his/ her ads will appear & publishers choosing which ads are to be published in his/ her website ?