Silverlight Beta 1 gave us the ability to set the ZIndex, but some investigation of how it actually works on a canvas is useful to get the result you might expect:
Things don't always work like you expect, and as in many other instances, forewarned is forearmed.
I included 3 canvases to show examples of the issues I worked through getting it to work the way I wanted.
Silverlight Web Articles I've tagged and My Silverlight Articles