Proto-Canada (because this was shortly before confederation and dominion status etc.) was actually pretty involved in the US Civil War, at least for a party not officially in the war, and proto-Canada sided with the Confederacy. I think the main reason was basically just that the British Empire wanted the USA to split in two, as a divide and conquer tactic. In terms of proto-Canadian involvement, it was both on land and at sea. Some CSA ships were allowed to conduct raids out of Eastern Canadian ports, using them to restock and avoid Union vessels, and there were also land raids launched out of Central Canada. See:
en.wikipedia.org
en.wikipedia.org
This is very much a little known fact even within Canada, because the Canadian neolib elite find it deeply embarrassing. Proto-Canada's allegiance to the CSA seems to have gone beyond mere geopolitical jockeying, however. Canada's most important founding father, Sir John A. MacDonald (whose statues have been getting torn down due to cultural revolution, as of late), is said to have so named Canada's confederation as an homage to the CSA, out of his deep admiration for the Confederacy. Additionally, I have heard it said that he partly modelled Canada's division of powers on the CSA's system. Canada indeed has more of what Americans would call a "states' rights" ethos than the United States.