Appeal to antiquity/tradition is the position that because something worked for us in the past we should continue to do it seemingly in perpetuity. This is problematic because it ignores the modern context. Just because something worked in the past doesn’t mean it’s still beneficial today.
In immigration discussions this fallacy manifests itself as the “Canada was built by immigration” meme. While it may be historically factual that Canada was built by immigration it’s not an argument for continued and ever increasing immigration in the present. This is because “current year” Canada is a different place than the Canada of one hundred years ago. We have to take into consideration the health of the economy, immigration’s impact on the environment, its effects on social cohesion, technology and its potential impact on the labour market, among other things.
To illustrate the absurdity of this argument we can perform a thought experiment where we imagine a Canada were every space of land is occupied by an individual so that you couldn’t take a single step in either direction without stepping on someone’s toes. It would be insane to continue to allow immigration in this scenario just because tradition demands it. If the country hadn’t become an undesirable place to live long before it got to that point it definitely will become an undesirable place to live when it does. The country’s economy, society, and institutions would have collapsed under such weight. I acknowledge this is an absurd example because it’s highly unlikely the country will ever reach that point but it does bring to light that population sizes do have their limits and immigration cannot be spoken of independent of a myriad of other considerations solely because it worked so well for us in the past. Canadians cities consistently rank in the top tier of best places to live in the world mostly because they are medium sized cities however unrestrained immigration will undo that. These once livable cities will become unlivable, a process already in the making for Toronto.
If we were to remain true to the "Canada was built by immigration" meme then we would be favouring European immigration almost exclusively because it wasn’t just immigrants who built Canada. It was European Christian immigrants who did.