Mark - I did Paris a few years ago and it was HOT. People(runners and spectators) were falling over in the heat. So I'd be prepared for hot or cold.
Good luck with the trio. I was tempted but decided just for Brighton and London. I must have been destined to do 3 marathons this year as I finally got into New York on guaranteed entry....... hmmm maybe 4 as Beachy Head is a nice day out.