I would go for a MTB-based cross bike, something like this Cube Editor: it has a solid aluminum frame, it has a carbon belt drive, so you never ever have to lube your chain, it is reasonably light at under 12 kg, it has a Shimano Alfine 11-speed shifter, has flat bars and is fully rigid. I personally don’t like how hub gears shift, so I would go with a 1x setup. But in terms of maintenance, this combo is hard to beat. Plus, the Schwalbe Marathon tires are indestructible, and because they are 42 mm wide, you will be reasonably comfortable. I would definitely put on fenders. In case you don’t like cycling backpacks, you’d also need a rack. I haven’t checked prices, but I would expect that the Cube costs about 1,200-1,500 €. (Edit: I was spot on with the price, I found it for 1,260 € online.)
If you go for a bike with a traditional rear derailleur, go for Deore SLX or 105: you get 95-99 % of the performance of the more expensive groupsets, and the only real penalty is weight — which in those quantities doesn’t matter enough for commutes.
There is a discussion of flat bars vs. drop bars, which to some degree is a matter of personal choice. I strongly lean in favor of flat bars: you have better bike control and given the speeds you will be traveling at in Paris, aerodynamics will be completely meaningless, unless you ride like a total hooligan. (If you are on a longer commute between cities where aerodynamics does end up mattering, this is a different story.)
I would shy away from a proper trekking or touring bike for two reasons: (1) It is way too expensive. If something happens to the bike, perhaps it gets stolen or someone kisses your bike while parking (I’ve been to Paris often enough to know that the locals park by ear), you will be really sad. (2) It is too heavy and has lots of features you don’t actually need. A Pinion gear box is neat, but you will never need the 600+ % gear range for your commute. (3) Forget about steel, carbon and the like. Aluminum is where it is at: it is the mass market material and aluminum frames are great and inexpensive. Steel frames cost more and you get no benefit while commuting (except for the feel of steel). Ditto for the even higher-priced titanium frames.