Hi James,
Most long term rentals will have high speed internet already installed, although you always want to check. Most places have cable internet and cable or satellite TV. Some homes in Grecia, as mine did when I lived there, use a service called CR Wifi, which uses microwave transmitters to provide high speed internet. You can find out more about them here: http://crwifi.com. The service was fairly reliable for us but we did have issues at times with using VOIP services like Skype and MagicJack, as well as streaming through Amazon Prime. Netflix and other internet usage was fine, if slower than cable internet.
The reason some homes were on CR Wifi is that the cable hadn’t reached that area/neighborhood as it was off the beaten path a bit.
Sometimes a landlord will pay the cable/internet bill or charge you directly.
If for any reason you have to have cable installed you can do so without being a resident. I’ve had cable installed in a few places and it’s never been a problem.
It is a good idea to have a backup USB plug in modem that runs off the cellphone network for the occasional outages.