The most pressing issue in Canadian tax policy today is that people don't like paying taxes, and it is increasingly hard to persuade them to do so.
The heavy duty engines of tax revenue generation are the personal income tax and the federal and provincial sales taxes. Federally, personal income taxes raise about half of all tax revenues. Provincial sales taxes raise considerably more revenue than provincial corporate income taxes. Yet these bases are eroding.
The most reliable payers of income taxes are middle-class salaried employees. It's hard to get the poor to pay taxes, because they don't have much money, and it's hard to get the rich to pay taxes, because they are mobile, and can take advantage of tax planning opportunities. But income inequality in Canada has risen, and relatively more income - thus relatively more of Canada's tax base - is in the hands of the elusive 1%. This income concentration partly reflects an increase in the share of Canada's GDP going to capital - and capital income is much harder to tax than labour income.
It's also hard to get the self-employed to pay taxes, because they can write-off home office and other everyday expenses against income. And the number of self-employed has been growing more quickly than the labour force as a whole.
But taxing the rich and taxing the self-employed is trivial compared to taxing retirees.