I'll argue that it was avoidable. Although there were many unresolved issues between the British and America by 1812, and tensions over impressment were running high, the Napoleonic Wars were nearing a successful conclusion for Britain and her allies, and one could easily argue that the British were quite tired of fighting, and paying for, long overseas wars.
With intensive diplomacy, and some compromise on both sides with regards to freedom of the seas and the Canadian border question, it was possible that the War of 1812 could have been avoided. Especially given the fact that little could be settled by war, and both sides knew that even as they began to fight in this conflict. So given a reasonable way out of war, I believe one side or the other would have taken it.