The very high levels of tax in post war Canada and the US are somewhat deceiving  as they applied to very high levels of income. A US tax rate of 53% in 1950 applied to incomes in the 38,000-40,000.  That translates to almost $300,000 today or much higher than Trudeau bracket of $200,000.  Also why didn't the US government collect more taxes from the upper income people, perhaps more deductions?  
One thing you are ignoring is that taxes have to be competitive. If Canada is much higher than the US than that encourages migration south of the border.