I have a valid Canada work permit till Sept of 2012. I am planning to go on vacation to the US. I am a citizen of the Philippines but I will be coming back into Canada from the US. Do I need a temporary resident visa to come back ? Thank you.

It may be possible to return from a short trip to the USA on the basis of an existing single-entry visa. However, it would be best if you confirm your situation with Citizenship and Immigration Canada to be certain.

I visited Canada immigration downtown and the lady said it should be fine as it says on CIC website

"If you are a citizen of a country that requires a temporary resident visa to travel to Canada, you must also have a valid entry visa to return, unless you are returning to Canada from the United States, Greenland or Saint-Pierre et Miquelon and the period initially authorized for your entry or any extension to it, as a visitor, student or worker has not expired. "

My concern is work permit is valid till September 2012 but multiple entry temporary resident visa is expired 2010. is this ok as long as the work permit is valid?

thank you

Based on the information you are supplying, this would not apply to you. A new entry visa appears necessary.

I went to immigration again and they said it was ok to go to US without a temporary resident visa even if previous one is expired as long as the work permit is still valid.
I was able to go to California for a week and come back with no problems.