Play a Madden 17 Trial
There is no Madden 17 demo or even a Madden 17 beta, but if you are an EA Access member you can play a Madden 17 trial.
You can play Madden 17 for 10 hours on the Xbox One if you are an EA Access member. This is the full game and all progress will continue towards the final release.
EA Access is $5 a month or $30 a year and includes a trial of new EA games before the release as well as a number of full edition older games, including Madden 16 and many others.
If you then buy Madden 17 digitally on Xbox One you save 10%, which is basically the cost you paid to try Madden 17. You also get 10% off MUT points.
The EA Access program is only available on Xbox One. There is no option to play Madden 17 early on PS4, Xbox 360 or PS3.