Certified GKH Gardening Expert
Milkweed tends to have a taproot, so they don't do as well in a container as they do in the ground. I have grown a few different varieties in containers with varying success. You may have to replace the plant yearly.
Monarchwatch.org says narrowleaf milkweed, Asclepias fascicularis, is good for the California Monarch waystation. It may need to be grown from seed, but check your local nurseries. The Xerces Society also recommends Kotolo milkweed, Asclepias eriocarpa, for Southern California. Monarch Watch includes showy milkweed, Asclepias speciosa, for Western states.
The tropical milkweed (Asclepias curassavica) does well in containers, but it is surrounded by controversy that you may want to read up on before deciding whether to use it. Since it doesn't die back in winter, a buildup of the harmful protozoan parasite OE can occur. Some recommend cutting it back a couple times during the summer. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=43489