Yes, I do believe that the majority of congress is opposed to the war in Iraq. I also believe that the 2002 AUMF is insufficient for continuing it. The AUMF is authorized us of military force on terrorists. For one, I believe this law is meant to focus on individual terrorists or groups of terrorists. I don't believe it is meant for a whole country. Also, the majority of terrorists are no longer in Iraq.
If Congress actually ever opposed the war in Iraq, they would have discontinued funding of the war from the get-go. But of course, they didn't. They didn't care that only Congress can declare war, they didn't care about the President gaining more and more power, because they supported the Iraq War.