No, that's completely disingenuous. Other factions have actual industry and manpower to fight other great powers, something Canada lacks, unless you think Canada, Australia, and French Algeria is a peer opponent to Germany. The CSA has a larger population than Canada, and likely more than the rest of the Entente combined, sans the Raj. New York has more people than all of Canada. Ohio has a larger population than all of Australia. This isn't hard to grasp. There are states in America with more people and factories than entire countries. Even if they send fifty thousand soldiers, they'd only have an advantage at the start of the war before the CSA begins churning out more equipment and better armed soldiers.
Realizing an invasion is hard doesn't equal having a military capable of pulling it off. Canada does have veterans of WW1 in the army, but lack the manpower or material to leverage it beyond small numbers. Canada is burdened by British expats running the show, lose of trade to Britain, and a downturn in relations with America is going to hurt an already fragile economy built on exporting to the imperial core. The British expats are unlikely to pursue a program of state directed industrialization necessary to expand Canada's existing industry, especially when mostly Tories fled Britain.
Even if Canada pursued an aggressive policy of militarization and industrialization at the cost of everything else, its forces would be smaller and less well equipped than CSA's army. The majority of America's war industries is in the CSA, so tanks, artillery, guns, and airplanes alongside a bunch of other stuff are in the CSA.
You do not understand the sheer amount of people and industry in the CSA. The AUS has racist militias and German support, but beside that they're running off hope and momentum. Feds have secondary, smaller manufacturing hubs in California and border states that haven't joined the CSA. Canada is a speedbump in this war. America was its last major customer too, so with the civil war breaking out Canada's economy is not going to be doing well.