None of the three factors mentioned in the lead post are fake. Good or bad, Mayor Plante ran for election on a platform that included a promise to hold a referendum if any taxpayer money was involved in building a new stadium. If she were to go back on that, it would hurt her with her base.
The identification of Charles Bronfman as at least a tax avoider and possibly a tax evader through the use of tax havens, as well as Trudeau's principal fundraiser, would make it difficult for the federal government to fund a stadium which would benefit him financially as an owner of the team.
The federal Liberals have been in power for most of the last century by adapting to what the voting public wants.
Montreal's deteriorating infrastructure is described in a city report in 2011:

Nearly one-third of Montreal's deteriorating road structures need repair work and a dozen of them are considered in critical condition.
That's according to a study that examined 555 pieces of infrastructure under local jurisdiction.
The report released by the city today found 12 were in the most critical shape, 44 were deficient, 38 were mediocre, and another 81 were just generally deteriorating.


That means just over 30 per cent of 555 structures such as bridges, tunnels and overpasses need work.
The city's chronic infrastructure problems were brought into focus this summer when a giant concrete slab collapsed onto a downtown expressway, while bridge closures caused monster traffic jams.
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Good or bad, the new mayor promised to push for upgrading the city's infrastructure. The federal Liberals would ignore Montreal voters' preference at their peril. Montreal itself is important to the Liberals reelection both federally and provincially. Trudeau himself is elected in Montreal. So funding Plante's infrastructure requests to some extent at least would benefit him while funding a new stadium for a crony, Bronfman, who is now known as a tax avoider would create political problems. I have heard a former elected Quebec Liberal on CBC's Power and Politics even acknowledge that the smart thing for the federal Liberals to do would provide some of the infrastructure projects Plante is requesting.
The new roof for the Olympic Stadium may have been in the works for a while but its funding will come out of current and/or future budgets, limiting the funding for other projects and raising questions about whether the provincial government has its priorities right if it funds another sports project, a new baseball stadium, while ignoring Montreal's severe infrastructure problems. Politicians who don't listen to voter priorities don't usually get reelected.
When Warren Cromartie began promoting a new baseball team does not affect these political realities.