Hi Francois,
Thanks for using Syncfusion products. The GridDataControl should work fine with any WPF Panel host. Do you want the columns to auto-size or just the GridDataControl to fill the space? If you want the columns to auto-size, we recommend you to download our latest ES 2010 Vol1 RC and check out the new column auto-sizing feature,
http://www.syncfusion.com/support/forums/general/92728/essential-studio-2010-volume-1-rc-release-v81026-available-for-downloadif it is the latter case, then you should probably set the Width and Height to Auto as you would do for any other WPF control.
Thanks,
Fahad