Canada has an immense unguarded border with a country that has several million uneducated people living in extreme poverty.

The US is the target country for most migrants, they don't continue on through to Canada in large numbers. If they did, most would likely get deported, Canada's immigration is highly selective.

It's again not quite that simple. Canada's asylum acceptance rate is higher than the US. However, due to a bilateral policy change in I think 2009 asylum seekers could no longer pass overland through the US and apply in Canada. This reduced the asylum seeker rates from south/central America and Mexico a fair bit to Canada as they were forced to apply in US.

Outside of just asylum seekers, although successful immigration rates are much higher in the US than Canada (about 4x), per capita Canada is much higher (as there is a 10x population difference).

> Canada's asylum acceptance rate is higher than the US.

Canada decides who comes to Canada to apply though (via resettlement programs where the seekers have been referred by a third party like UNHCR), it's generally not that people just walk across the border as they do in Europe or the US. If you can choose, for example, to resettle a bunch of academics and their families from Afghanistan, you are in a very different situation vs having the average Afghan population show up at the border which includes a large amount that are functionally illiterate.

This isn't a critique of Canada's selective policy, it's just a very different situation, much like somebody who lives in a rich part of town will not have to deal with the same issues as somebody who lives in an area with high poverty even though they both go to work, buy groceries, take showers and talk to neighbors.

That's mostly true these days although more people did used to just show up at borders and ports of entries, prior to the policy changes I mentioned.

There has been an uptick in recent years also, primarily from the US (but also some sea ports).