By the time they take control (which taking enough interest to show up at the polls; they've had the numbers for a while) the only real tax route to slam boomers (who as a group will no longer have an working income) will be an estate or inheritance tax. That'll be bittersweet.
A 20% estate tax would take a massive chunk off government debt over a 20 year period; likely around $600B for Canada (inheritance runs around $75B/year right now; inflate by 10 years to roughly $150B/year if markets/housing doesn't tank and take 20%).
There are other ways you can do it though besides taxing. You can gut CPP, you can reduce subsidies for retirement residences, you can reduce subsidies for prescription drug plans, all under the guise of reducing government expenditures. Not that any of those are advisable (or politically feasible), but there are other ways you can hit boomers without doing anything with income tax rates.