Situation is tough. Two of the biggest agencies are Hertz and Sixt, which on Corsica are owned by the same people.
There are widespread reports of Hertz and Sixt forcing electric cars on people who go there expecting to get a standard, small car.
Instead they are offered a take it or leave it Renault Zoe, a smaller EV that apparently seats only 4 people and has limited luggage space.
To get an idea of how common this problem is, look at the Google reviews for Hertz offices on the island, such as this one for Hertz at AJA airport.
You can sort it by newest and see that this is a widespread practice.
Some of the reviewers say that they are told there are plenty of chargers on the E-Motum network but find that a lot of these charger locations are not yet installed.
It turns out the owners of the island franchises for Hertz and Sixt are also owners or investors in this E-Motum network. But also, there may have been govt. incentives to purchase EVs for rental car fleets.
I basically decided to write off a visit to Corsica next month. Instead I'm going to just visit the Italian and French Rivieras. I've been to the latter many times, never to the Italian side of the border.
But I keep searching different car rental booking engines, such as Kayak, Rentalcars and AutoEurope. But most of them only return results from Hertz, meaning you will end up with an EV and uncertain charging status, since the places you visit may or may not have chargers available.
I've been searching up through next April and it's still the same situation, either not available, available for a high price or only Hertz results where the prices are okay but you expect the same situation, being forced to take an EV or not having a car.
Especially more limited if you look for automatic transmission. Some of the reviewers complain that they reserved a manual transmission car and end up with an EV which is automatic.
I don't know if the situation will improve. It may or may mot be impacted by the pandemic so they may have problems adding more gas cars to the fleet. Personally I'm for EVs but the charging situation doesn't seem good for long-distance travel, when you can drive 200-300 kilometers in between some cities on Corsica.
I also checked the rental car situation on the mainland. Some offices have EVs but when you choose cars, the EVs are clearly identified. In theory they can substitute an EV but there are no reports of this practice. The other thing is, the charger situation on the Cote d'Azur is no better. A lot of the chargers are at hotels and supposedly, they prioritize their own guests at those charger stations on their property, if they allow non-guests access at all.
So I don't know when I'll be able to visit Corsica again, with some certainty that I will be able to get around at least parts of the island, not worry about whether I have to spend hours looking or chargers or leaving the EV charging.