Any way to change the default canvas parent when opening UI prefabs in the new Prefab editor.

The new Unity Prefab workflow is excellent i use it all the time when changing in game objects. However when it came to creating UI prefabs as i want to load some in and remove some at certain points im getting a weird issue. The Canvas size of the Parent that you get is different from the canvas size i am working with. This results in very weird scaling issues. Is there any way to change the default parent canvas fro prefab mode or am i just going to have to change my own to match it ?