The main reason, outside of the issues of neutral shipping, that the US was upset with Britain during this time had to do with British forts and Native Americans. The British had maintained forts on US territory even after the US became independent. This was a severe infringement on US sovereignty. It was compounded by the fact that the British were using these forts as places from which to arm Indians and encourage them to attack American settlers. It was intolerable for Americans that the British would be doing these things on American soil.
There were also some Americans who wanted the war simply to be expansionist. This was one reason that some Americans wanted to invade Canada. However, the much more important issue was the issue of the forts.