Department of Finance has done extensive modelling. The whole fallacy of calling CPP contributions a tax is that it ignores the benefit side that comes from higher contributions. Benefits will increase. Incomes will increase and consumption expenditures will increase, and that has an impact on output, on employment, and the like. That's why in the medium to long run, there will be a net benefit from expanding the CPP.
On November 15th, 2016. See this statement in context.