Its interesting how much French electoral geography has changed. When Mitterrand beat Giscard narrowly in 1981, he won big places like Pas de Calais and in Provence (esp. Marseille)...Giscard on the other hand did best in Brittany and in Paris itself...now that is all reversed
It can be explained as Macron seems to be a 'successor' to Giscard more than 1981 Mitterand, at least in rhetoric. Pro-EU, liberal, cosmopolitan. Basically the benefactors of the ordo-liberal system, which includes the CAP subsidies. '81 Mitterand was mainly courting the 2nd round PCF vote. On the other hand I think this election really demonstrates how French political consciousness has changed, and its political landscape with it, making the comparison moot.
Anyway, I think parochial boy's predictions are the closest I would go for, except for Fillon. His will be somewhere rural in Alsace-Lorraine, or Sarthe as Kringla says for a home effect. Its true that he has the Estrosi effect in Alpes-Maritimes but I think Le Pen will do really well in the first round there.
I think Mélenchon's best will be Seine-Saint-Denis but paradoxically in the legislatives his France Insoumise candidate will have their work cut out in Montreuil against the Greens and PCF, who are both running candidates against him. The radical left need to get their sh**t together.