That’s not possible, at least not out of the box.
While you could query the page chosen in the ville field, the options in the lieu field will only be updated after saving.
So you would need a custom field that listens to the first field changing.
See also this post: Programmatically change the content of the file field - #38 by bastianallgeier
However, I wonder if when you don’t use a query in the blueprint, but do the querying in a second field directly in vue, this could be solved without saving first… 