For the record, I think Canada, was doing this all pretty well until maybe the late 1970's, even maybe until the late 1990's to a certain degree.
We have been the most accepting, tolerant, and multi-racial country in the history of planet earth. I don't think there is anything wrong with that. You encourage ppl to unite under nationalism, language, and religion, if not religion then a common cultural creed/ethos... you encourage integration into the common culture, but sure you can keep flavors of your original culture and mix it all up. Then you can get the same result as places like Korea, Japan, Singapore etc... Because then "out of many you are now one". You go a bit slower with immigration into the country to allow this to happen naturally. That seemed to be the idea, it was working until it started to erode slowly in the 1970's and vanished completely 5 years ago when Trudeau was elected and he announced we are a post national state.
If you don't do any of that you just end up with a massively divided and frankly very confused population. Divided on so many levels it's not possible to function as a unit under any sort of stress test. It's never worked in the history of mankind. My hope is that this event is a massive reset and re-think on a lot of Leftist ideas about society and culture.