The Americans like to pretend that the causes of the War of 1812 were naval, arising from the Napoleonic Wars.
There were some naval problems of course,
Basically the RN was enforcing a blockade on Europe that the US believed was interfering with US trade ... which it was to some degree.
The RN knew that the US ships had many British born sailors ... which they did.
American practice regraded these as US citizens - despite teh fact that in most cases the US refused to write formal papers.
British law did not even recognise the individuals right to change nationality without permission.
Therefore the RN regarded such paperless Britons as 'draft dodgers' or outright deserters and therefore arrested them when found.
Of course, the real US war aims were a simple land grab north.
In OTL they believed they could manage this because the British were tied up with Bonaparte for the foreseeable future, who still looked invincible in 1812.
Assuming the OTL immediate disputes were settled
(as they well might have been. Delegates actually agreed terms twice only for one or the other Government to send them back)
Hostilities might well have been delayed ... with no losers , except possibly Bonaparte
But ... would the Americans think the same in 1817? after Waterloo (or TTL equivalent?)
Personally I doubt it but if they did I would expect the results to be initially around the same.
Canada could be held against any initial US attacks.
While it is true the British had demobilised both their Army and Navy very quickly in 1815
the actual in place garrison of Canada was about the same in 1817 as 1815 and the potential reserves proportionally much higher.
Conversely there is no reason to expect the US Militia forces to perform any better than they did in OTL.
(were there 4 or 5 attempts all repulsed?)
At sea, the RN local squadrons were at "peacetime" levels in OTL and would be similar iTTL.
They were rapidly reinforced OTL and that would again be true.
While there were far fewer RN ships ships in commission, these tended to be the better designs and captains.
Equally there were many more in reserve.... and most still in good condition.
Overall, without the distraction of 100 French battleships and 100 French frigates, I would expect the RN to deploy more and better forces ITTL. Therefore the USN
might still have some initial successes but as in OTL would eventually be destroyed or driven into port.
British sea trade would be less well escorted initially (simply less RN ships at sea) so more USN success raiding but US sea trade would be ruined... perhaps no quite so quickly as OTL, but just as completely within 2 years.
The Big question, is would the British stop their counter attacks as in OTL ?
OTL they were basically resource limited until 1814 and might still be in 1817 (though for different reasons).
However By 1817 both the the Admiralty and Horse Guards were looking out for an excuse to reactivate more forces,
so I imagine by 1818 more British regiments would be arriving
and with no "Spring Violets" in 1819 more US cities would burn before peace broke out.