Justin Trudeau has spent three years saying his central focus is on helping struggling, middle-class Canadians; on Monday he'll finally start explaining precisely how he intends to do that. The Liberal leader is set to unveil a major economic plank that will underpin his party's eventual platform for the federal election scheduled for October.

The details have been months in the works, tapping the expertise of a dozens of economists, and are a tightly held secret.

But Liberals have been hinting that they would rejig the universal child benefit and the tax system to put more money in the pockets of middle-income Canadians.

They've also not ruled out increasing taxes on the wealthiest Canadians.

Trudeau has already said that a Liberal government would scrap the Harper government's plan to allow income splitting for couples with young children for tax purposes and would reverse the recently announced plan to almost double the amount Canadians can sock away in tax-free savings accounts -- measures which Trudeau says will primarily help the wealthy.

Doing away with those two measures would give a Liberal government about $3 billion a year with which to finance its own program, which Trudeau has promised will be done within a balanced budget.

Time is ripe

Since he first launched his bid for the Liberal leadership almost three years ago with a pledge to focus like a laser on the plight of middle-class Canadians, Trudeau has been criticized for offering few details about what exactly he'd do. He's resisted pressure to unveil his platform before the election, arguing that he wants to develop policy from the ground up, not top down.

However, with the Conservatives' latest budget finally unveiled late last month, the Liberals have determined that the time is ripe to provide details of their alternative to the Tories' re-election economic plan, which pivots around parental income splitting and a boost to the monthly universal child care benefit.

In a "sneak preview" email blast sent out to supporters Sunday, a video message from Trudeau says the "major announcement" he's about to make is the result of listening to thousands of Canadians in hundreds of communities across the country.

"The message I hear everywhere is clear: Canada's economy has become a lot less fair with Stephen Harper in charge and something must be done to fix it," he says. "Tomorrow, we'll take the next, big, positive step in that new direction."

He urges supporters to watch a livestream of the announcement "to hear about our plan to provide fairness and growth for the middle class and those working hard to join it."