I have a question! URGENT!

OK; so I am going to St.Louis for voluntary opportunity.
They offered me the position with at least 1 year work.
However,when I tried to apply for us visa, B1/B2, I was not able to.
Beside, I just heard that I can't even stay more than 6 months.
Is there any way I can stay 1 year? Should I come back to Canada and go back again? Besides, this employer asks me to send them any official document that guarantee to stay for certain period of time but where do I get such document?
Isn't it I'm just going to the port, they say I can stay for how long or not?
It's really hard to get answers from US consulates. Plz help me!
thanks in advance

Mate.
Don't be crazy. Do not work in the US or any other country without a proper work VISA! It is a quick way to find yourself on the wrong end of ICE (Immigration Police). I hear the meals are not good in prison.
Also, you get yourself out of this country (US) for a minimum of 5 years. Not worth it.
You must exit the country 6 months less a day without a Visa. The actual details around how long you need to be out between times are best left to Lawyers.

Volunteer or not, a job is a job to the INS. Getting paid for it is something that the IRS worries about. If you cannot get a VISA, then I suggest taking a free trip and enjoying a few days in St Louis and call it a day. Cheers and good luck

Yea, but they have done it two years ago, and they even sent me the invitation letter to present at visa interview. Besides, it clears states that I am not paid. Anyway, is there any government agency that I can check with? Should I go to US consulate?
Thanks for your words.

You cannot work, not even volunteer, in the US without a proper work authorized visa. check out this recent article about volunteers who wanted to go help re-build New Orleans.

You need a work authorized visa of some sort, and the organization that you're going to volunteer with needs to sponsor it. If it is a religious organization, there is a religious/missionary/volunteer type visa, but I can't remember what it is called. Make an appointment at the consulate and ask them about it, and find out what you'd need to qualify for it.

Canadians are exempt from getting a visa in B-1/2 visitor status. But as Reba says, even in a volunteer position you need some sort of work authorization usually.