What is my visa status when canceling a Work Permit and can I apply for a new one on the same day?

There is a difference between a work permit (I'm guessing that's what WP is short for), a Non-B visa (that allows you to work in Thailand, sold as either a single entry 3 month visa, or a 1 year multiple entry visa with a 90 entry each time), and an extension of stay based on employment (that allows you to stay in Thailand for a year).

AS OF TODAY:

For question 1:

IF you have a Non-B visa and DO NOT have an extension of stay, your entry on the Non-B visa will continue being valid until the date on the "admitted to" stamp. After that date expires, you will be on amnesty, which will let you stay NO LATER THEN July 31.

IF you have an extension of stay based on employment, when you cancel the extension of stay you will automatically go on amnesty, letting you stay NO LATER THEN July 31.

For question 2:

The benefit of getting a new extension of stay the same day you cancel the old one is so that you don't need have to leave Thailand, purchase a new Non-B visa, and get a new extension of stay.

and the real question IS

are you on a Non-B VISA

OR

are you on an extension from the immigration office