It doesn't matter unless Trudeau was raised knowing his ancestry AND believes the same and has the same sort of goals. Which is a lot of assumptions. If those things aren't true, then why would it matter other than personally to him in the sense that people want to know their ancestry? Who the parent is doesn't necessarily reflect on a person's beliefs or anything. Especially if that person didn't even know. I'm not saying he didn't know (if it is even true, which yeah, it looks pretty convincing), maybe he did, maybe he didn't. But for it to matter at all, he would have to have known and also decided he was going to align with the agenda of the person who didn't raise him. Political/sociological belief system isn't genetic.
But also just food for thought, with the understanding I am not saying this couldn't be true and even probably is given the visit to Castro by his mom... some people are just doppelgangers. I had two friends named Justin R (both had last names starting with R). One in kindergarten, and one later in grade school. I seriously thought, in my little kid brain, that they were the same person. They were both Justin R, and they looked fucking identical. Well in high school, the original Justin R, who I lost touch with after kindergarten because his family moved, moved back to the area, and I encountered both of them at the same time, and it blew my mind because the whole time they were different people, but put them next to each other, and they were identical twins. But different last names, different parents and grandparents, also a couple of years apart, but probably both families ancestrally from the same area or something. The resemblance was so striking that everyone joked about the two Justin Rs being long lost brothers, but they insisted they were not related and didn't have common ancestors, up to great grandparents anyway.