Aside from soaking in water, any treatment to wicker before weaving to avoid breaking?

Answer 1

Wicker is any sort of hard woven plant fiber and comprises many different species. There's a great article here about wicker, including the most common plants used.
http://www.wickerpedia.org/wiki/Wicker/

Some species bend easily without breaking, others need to be soaked or you can use a steambending method, similar to how woodworkers bend wood using a steambox. Here's an article explaining in more detail how a steambox works and how to make one.
http://www.diybob.com/steambox.htm

Answer 2

steam