Enough left over for priority spending is an interesting statement. I agree with your premise that sufficient funds could be raised however I think the way you show it is very flawed and undersells just how large of change it would be.
A UBI only replaces
OAS/GIS 50 billion
CPP- 50 billion
EI - 20 billion
RRSP tax deductions 23 billion
Child benefits 23 billion
CPP current fund of 355 billion at 3% per year 10 billion
So you have access to about 180 billion so need 220-300 billion more.
Health, Education, transportation don’t disappear as a result of a UBI. You can’t just say of 26k per year 20k is available to give away. And if you are saying that then you are actually decreasing the amount of money lower income people have as a bunch of it gets sent to people who already have higher income. So whatever math you are using you can only use funds that are directed for living expenses and replace those unless we are moving to the pure libertarian version of UBI where health, education, garbage collection and security are no longer provided by government
I think a better way to think of the governments capacity to raise taxes is to compare the % of GDP used by government programs. Canada is 40%, US is 35%, Sweden is 48%, Finland is 53%, France is 56%, Germany is 45%.
https://en.m.wikipedia.org/wiki/List...centage_of_GDP
Our GDP is about 2.1 Trillion Canadian so 1% increase in public spending as a % of GDP is 20 billion. So if the Canada chose to become among the most socialist large nations (And assuming no impacts on GDP for now as a result of this grand exeperiment) you have the ability to raise about 320 billion if we move to 56% of GDP spent (really more redistributed) by the government.
Which does get us to the threshold to offer every adult a UBI.
To hit your 20k figure and 400 billion we just need to collect about 50% Of GDP in terms of taxation which in Europe is still high but certainly not an outlier. I think politically canceling tax breaks on RRSPs and nationalizing the CPP would be significant policy problems.
The problem with UBI that doesn’t get discussed much is that if you if you price you price it low enough so a couple is still incentivized to work a single parent is likely still in poverty and you have canceled all of the income based programs to fund UBI.