1. As far as I know, you would need to select and cut the items and then paste them inside a new Drawing Canvas.
2. It is also not apparent whether you can set a default for new Canvas Items.
However you could use a macro to create a new drawing canvas with your preferred 'default' fill AND if you have selected shapes before running the macro, those shapes could be put inside the canvas by the same macro.
Code:
Sub AddInlineCanvas()
Dim shpCanvas As Shape
Set shpCanvas = ActiveDocument.Shapes.AddCanvas(Left:=150, Top:=150, Width:=144, Height:=144)
With shpCanvas
.WrapFormat.Type = wdWrapInline
.Fill.ForeColor.RGB = RGB(220, 40, 0)
If Selection.ShapeRange.Count > 0 Then
Selection.Cut
.Select
Selection.Paste
End If
End With
End Sub