The content offered as DLC in Japan will be on-disc for the US release.
http://www.nintendoworldreport.com/news/24106
At a Samurai Warriors 3 game night today, NWR learned that the downloadable content for the Japanese release will be included on the disc for the North American version. The Nintendo game page also states the inclusion of the DLC content (Historical Mode).
Previously, the Samurai Warriors 3 box art for the North American release was noted to have no orange Wi-Fi Pay & Play logo as the Japanese box art does. The paid downloadable content gives you an additional "Historical Mode" where you can play with a custom character in three additional chapters, each with five scenarios, for 300 Points per chapter.
The European release from May this year also has the Historical Mode on disc instead of as DLC, as well as an online co-op mode, not present in the Japanese version, that is also included in the North American release on September 27.