Electronic program guide with display of alternative-source multimedia program options and estimated availability parameters

An electronic program guide ("EPG") coordinates the display of availability metadata representing the availability of listed multimedia programs from one or more alternative content sources. The EPG presents multimedia programs available from a primary content source. A system identifies alternative content sources for one or more multimedia programs listed in the EPG, estimates availability parameters from these alternative content sources, and supplements the EPG with availability metadata that represent the determined availability parameters of the versions of the multimedia programs from one or more alternative content sources. The system estimates missing availability parameters based on application of one or more availability rule sets, which can reflect, for example, a contractual agreement or arrangement, a data analysis performed on historical availability data for the multimedia program or the content provider, and the like.