What do producers provide for contestants in the event that a reality show gets canned after three episodes?

Answer 1

Read the contract.

Answer 2

Hotttotrot's got it. It's never the same.

I'd suspect that celebrity participants in a program would have more provided for them in the event of a cancellation rather than a handshake and a "so long."

Reality contracts for ordinary Joe participants usually stink. Some even stipulate that while you're competing and not being paid so much as a stipend that you are not allowed to use your experience on the program for later monetary gain, as in writing a book about or touring to talk about your experiences.