Union is suitable to platforms that are hard to achieve and / or involve high costs. For PC you should try Steam, Mac Store and similar platforms.
You need to have a successful game first before you can think about Union.
If you want to get your game published as quickly as possible, Indievania (http://indievania.com/) accepts anything and everything. Desura (http://www.desura.com/) also accepts just about everything and has a reasonably sized fanbase. Steam Greenlight (Steam Greenlight) is also an option, but the chances of anything getting accepted on there are quite small.