After an intense weekend of figuring out .sga files, I've finally managed to convert Dawn of War III's campaign missions into playable multiplayer maps.
I'm surprised I'm the first one to do it, but I'm more than happy to open up those tools to anyone that's interested in seeing how much effort Relic puts into their maps (It's a lot).
First: http://steamcommunity.com/sharedfiles/filedetails/?id=926708438 for those curious or would like to provide feedback.
I thought I'd take a moment to share how I did it and hopefully remove the headache for anyone else attempting.
If any of you modders remember older games, @Corsix has linked me to an .sga view tool we can use to look campaign files.
This tool can be found here: http://modstudio.corsix.org/dow3/SgaViewer.zip
Extracting into a seperate folder. I found a map I wanted to use, and brought over the .SCENARIO file as well as all the other .layer, .info, .exclude files that came with it. I put all of these into: C:\Users\XXXX\Documents\My Games\Dawn of War III\modssource\scenarios
Opening up World Builder, you need to navigate to that folder and should see the .scenario file. You will also need the other files associated with the .sga you're trying to lift in that folder as well. I was able to successfully import the map.
You'll still need to have a core competency for building maps. I recommend both community member
Draimond as well as Relic's Wiki on getting started.
After you're ready to import, go to Scenario Properties and ENSURE you've selected Multiplayer, as these maps are not marked for multiplayer by default.
My map is located at: http://steamcommunity.com/sharedfiles/filedetails/?id=926708438 for anyone that would like to see what a campaign map would look like in Multiplayer.
Let me know if you'd like be to convert the whole campaign.