Welcome from the "Northern-most state of the Confederacy"....Canada
(please, I hope nobody takes offence at that).
UCVRELICS is right...it is a Pattern 1853 Enfield made for the British military. It's not just the lockplate that identifies it as British military, but also the markings on the barrel. However, I can't tell you if its Type 1, 2 or 3 because you haven't given us a full-view picture. Please post more pics.
Value will depend on many things, like whether the lock functions properly at halfcock, fullcock, firing; condition of the inside of the barrel and the outside of the barrel (including underneath where it's hidden by the stock), whether all the parts are original, etc, etc. Can you see any rifling? do you have the original ramrod? etc etc