The tensions between the French speaking,Catholic descendants of French colonists and the English speaking,Protestant British population and government.
Ideas that the USA was planning any invasion of Canada in 1865 or just after are nonsense - Britain had sold far more war materiel to the Union than the Confederacy during the Civil War,the Union army was needed to enforce Reconstruction on US citizens in the South,and any war with Britain would have seen the huge British navy establish a blockade of the US coast and cripple the US economy - as it had done in the War of !812.President Johnson was aware of all of this,so had no intention - or desire to - attack Canada.
