Didn't Canada go early on because they were part of the Empire still?
That was a true for the first world war but Canada entered the second world war as an independent nation.
And yeah, like the US helped a lot but that's mostly because they walked in at the end with a fresh army after everyone else had years of fighting. It's very American exceptionalist to narrow the "victors" of WW2 down to the UK, the USA and the Soviet Union.