How are you going to blockade an almost 9000 km long border(with a huge variety of terrain) and a 243,000 km long coastline? The US can't even stop drugs and people coming through the 3,145 km border with Mexico. This argument also presumes that no Americans would smuggle supplies to Canada which seems unlikely to me because lots of Americans & Canadians are either related or friends.
Keep in mind the Canadians burnt down the Whitehouse. Twice.
Then simply marched back home and said “stop being so stupid.”
Not quite. Late in the war, the British Navy landed British troops who burned the White House.
About 85% of all Canadian militiamen remained at home when called up in 1812. In 1812 and 1813, British regulars and Indigenous warriors (from both the U.S. and Canada) invaded Michigan and Ohio, but didn't get any further than that before the U.S. counter-attacked.
A lot of Canadians talk big talk about some sort of insurgency like Iraq, Afghanistan or Vietnam but all those places have borders with other countries that can enable smuggling of supplies to the resistance.
Canada will be blockaded and after a period of cold and hunger the Canadian people will give up.