It is only a few years since the introduction of WiFi (Wee-Fee) into Paris hotels was a vital USP, something to be drawn attention to. Now, WiFi is just about everywhere: almost all hotels provide free WiFi at some centralised point, such as a lounge, if not in all the rooms, which is increasingly becoming the norm. And, usually, it's free, although a few places do make a nominal charge.
But if you can't get WiFi where you're staying, then you have a number of other options: the ubiquitous McDonald's (McDo, as the French delight in calling it), with over 800 outlets in France, and Starbucks notably in Paris and a few other cities.
Two other fast-food outlets that provide WiFi are Quick, which has more than 500 outlets, and the new kid on the block 'flunch', a fast casual restaurant change generally confined to shopping centres and autoroute service areas.
Elsewhere, there are numerous connections to WiFi, but many are password protected; so, you'll need to ask if it's possible to connect.
Almost the whole of France is, however, covered by 4G or 3G. So, if your mobile phone is enabled to accept 4G/3G connections, then this is a good way to connect to the internet without incurring roaming charges – be sure to turn off Data Roaming on your device. See this map of areas covered by 4G and 3G.
If your device is not 4G/3G enabled, then you might consider getting your own Travel WiFi hotspot device (www.travel-wifi.com). A Travel Wifi mobile hotspot is a small wireless modem that connects any Wi-Fi enabled device to 3G/4G Internet, with a fast and secure connection. For instance, you can connect your laptop, your tablet or your smartphone to Internet while you're in France, thus saving you a lot of money in data roaming. It comes pre-configured, and doesn't require any installation!