This is pure bullshit. His advisors and his predecessors had to know that there were international treaties in place that forbade the legalization of marijuana.
This isn't America where states rights rule. So, those honest Liberals either let him campaign on a complete lie which would be unconscionable for a party with that much integrity or, Trudeau willing went along with the ruse to get the young peoples vote knowing full well he wasn't ever going to implement that policy.
Either way, he's broken yet another promise.