Before starting, I want to say I know there is a 2 century long debate about who won the war, but frankly I don't want this thread to host any of that boring actual history stuff.
So whatever the Britain achieved in the war IOTL they need to achieve even greater success with great land and naval victories and possibly not only settle borders dispute totally on their favour(New Brunswick, Illinois territory) but also take some land, for example Northern New York, Michigan, Wisconsin, Minnesota and maybe settling the Western border a bit more south. Not all of those are as likely but they are just to illustrate the scale of victory I'm searching for.
Earliest POD allowed is in 1805, so you can settle the war in Europe to be favourable to Britain or settle US politics or declaration of war to line up with some favourable condition in Britain, basically you can move the pieces a bit before having the war, so the only thing that needs to happen is a war on the scale of the one IOTL and having the British achieve a decisive victory, but you can change the motivations for the war and add participants even.
P.S: The WI tag is there also because it would be interesting to discuss the consequences of the war, in the development of the British North American colonies and in the USA and of course all the fun stuff like any further conflict between Britain and Spain/Mexico, Britain and the US, Us and Spain/Mexico and the Slavery issue and possible alt-civil wars.