>

Nope.  Not in the slightest.
I can think of 4 factors:

Language: English, French, and Spanish are present in tons of countries globally, whereas German, Scandinavian languages, Slavic languages, etc. have very little presence outside their home countries. People from Africa or the Indian subcontinent are highly unlikely to know any Scandinavian languages, and much much more likely to know English or French.
Merit-based Immigration: Canada has a point-based immigration system. You get points for having higher education, points for knowing English, points for knowing French, etc. More points, higher odds of getting immigration approved. Canada of course does take refugees, but most immigrants are pre-filtered to be ones who will likely contribute to society and likely not detract from society. Maybe the term "merit" is an over-simplification, but that's the gist of the idea.
Geography: Canada, UK, and Australia are harder to get to for people that don't already have some stability in their lives. They're obviously not impossible to get to, but it's easier to get from Africa to Italy than it is to get to the UK, and easier still than it is to get to Canada, the US, or Australia. If someone from India is going to get to Canada, they probably already have means and some stability in their lives, or an existing support structure in Canada who is helping them out.
Ethnostatism: Many countries are, by default, ethnostates. Their lands is the land of a particular ethnic group, with a particular language, and a particular culture. But countries like USA, Canada, and Australia in their current forms are not like that. These countries obviously have indigenous populations but they don't run those countries' governments. American is not an ethnicity, it's not a language. Immigration to America is not as existential a question for America as it is for most European and even Asian countries. Another way to put this is that America, Canada, and Australia are "nations of immigrants" whereas most countries are historically nations of a particular ethnicity which happen to have immigration. >

I think you're spot on, especially with point 4.
I do have one small, pedantic nit to pick with point 4 though. What you describe there is a nation-state, not an ethnostate. An ethnostate is one where citizenship is restricted to members of a particular ethnic or racial group. >

I'm not aware of the nuances of the argument, bit I had a related quibble with item 4. Great intellectual argument, but to me it just boils down to ' not used to foreigners'. Now you can argue why, bit that is the basic.
I feel the same way when people describe Sweden or Netherlands as liberal. Now there is nuance in that argument, bit to me those cultures tend to be inherently conservative, with the huge exception of what YOU do is very much your own business, not something for them to weigh in on.. >

My assumption for Canada, Australia and the US is simple: they’re not native to their continents. Americans, Canadians and Australians all are immigrant societies. So over time they’ve all developed strategies for embracing outsiders.
The UK you could argue as a byproduct of their vast Empire, it was bound to import talent from all corners of the Earth when it could, and therefor eventually has its own style for integration. Also the UK has always made it a thing to not be “lumped into” the “European project”.
Europe has very clear and historically formed borders through a lot of blood and conflict and so their sense of identity is a little different and while European identity is a thing it’s definitely more rigid than Canadian or American identity, for example. >

Am British. We used to describe ourselves as a mongrel nation. Historically we were invaded by the Angles, Romans, Saxons, Vikings and Normans. We’ve been ruled by Germans. The Spanish sent a fleet against us which was wrecked, and the Spanish sailors integrated. 
Then we had the empire and people came from all over the world.
Nowadays we have lessons in school about multiculturalism. It’s a massive deal and really important to us. >

Then why'd you send all those refugees to Rwanda? >

To be fair, we haven’t actually sent any refugees to Rwanda. >

plan to. My bad, I wasn’t aware of the court delays >

The home office wants to send them there to discourage dangerous small boat crossings. It's with the courts at the moment. 
There's a big problem with human traffickers in Calais sending folks out in little boats with fake lifejackets. Lots of them don't make it. I don't think this is the right solution though. >

A big difference is the starting point. Canada and the U.S. were never completely a common peoples with a common culture compared to some Northern European countries. "Assimilation" in Canada/U.S. might just mean assimilating to a regional subculture or a particular city's subculture or an ethnic subculture in a big city like New York City. There's always been some wiggle room (especially in the U.S.), even if it was at the margins. Less than one generation might be enough to sufficiently "assimilate."
Since Northern European countries are much more homogenous, "assimilation" is a higher bar and might mean adherence to a very specific culture (even down to how people look) in a way that is nearly impossible for an outsider to really achieve. Even for second gen+ immigrants. >

I don't buy this. Italy only unified in the second half of the 19th century and the various states and regions still have distinct culture and pride for their particular region that is as strong as you see in the US. The history of Germany is all over the place and is deeply connected to empire and there are deep and enormous cultural divides between primarily catholic and primarily protestant regions. 
Neither of these countries are scandinavian, but both have similar anti-immigration sentiment within their politics. >

That may actually strengthen point 4. As you point out, Italy and Germany didn't unify until the 18th century. Because of a lack of historical continuity for these states however, their founders attempted to tie these countries together with the idea of a shared nationality. The concept of nationalism and nation states were actually first coined to describe the process by which both German and Italian speaking states unified in the late 1800s. >

But this is true of the US too.