Stamped B2 status on my canadian passport

Hello
I am a Canadian Citizen (I have both the Canadian citizenship and the Canadian passport). I got my citizenship by virtue that my father is a Canadian citizen. I was born and lived all my life in Pakistan and never traveled anywhere. On the 25th of June 2011 I traveled on my Canadian passport to the US. The Border security force official stamped on my Canadian passport a B2 visa and wrote a period of 6-months for which I can remain in the US (i.e. 24th December 2011).

I now have traveled to Canada on the 26th of July 2011. My passport was not stamped at exit in the US nor on entry into Canada. Here are my questions:
1. Now that I am out of the US, is the B2 visa on my passport still continuing or it has ended.
2. I plan to travel to the US in about a month’s time. Then if I am not stamped on my passport, then till when I can stay in the US

Thanks a lot
A. Moiz

If you were not given an I-94 you have nothing to worry about. Canadians do not need stamps nor do they need I-94's. There was probably a reason they stamped your passport, but if they gave you no special instructions, it means nothing. We have access to canadian resords and can see when you enter Canada. I don't think you have anything to worry about.