ESTA needs to be valid upon arrival in the US
This is really confusing that your US ESTA needs to be valid upon the arrival in the US as later on while you stay in the US your ESTA can get expired and you won’t be having any problem in leaving that country.
The higher authorities are of the view in which they believe that you are still adhering to the conditions of the visa waiver program, and so the 90 day time period is still valid for you. The most important thing that you must keep in mind is that you are not allowed to apply for eta Canada while staying in the United States or any other kind of travel authorization.
ESTA is not a visa:
As the visa waiver program allows the citizens of the 38 countries to travel to the United States without a proper visa for pleasure and business purposes. And the citizens have to be back to their own country within a particular time period. And on the other hand, if we talk about visas, well it is a long and a costlier process as compared to etias application.
There is a huge difference between ESTA and visas. You must know all the rules and regulations of ESTA when to apply or what is the particular time period under which you ave to come back to your own country.
Also Read: http://facebookhitlist.com/profiles/blogs/characteristics-of-the-visa-waiver-program-and-esta?