The point of the Death March was always to hammer home just how sheltered and idealistic the island kids were.
Sure, Hester had tried to nuke em once or twice, but this was meant to be the first real taste of what life is like for people who didn't get born on magic peace island with camouflage. It shows how each of them handle it.
It mind breaks Akira, Hirito's naivety gets him killed, Kazuki basically constantly puts himself in situations where he doesn't actually have to deal with any of the actual moral problems, and Maya and Soushi are left to clean up the mess. It's there to remind you that the Earth actually is fucked. Humanity literally does only survive in tiny little highly protected pockets of civilization and if the protections fall then both other humans and Festum will be quick to pick off the weak.
Canon's Power operates under what is basically a Selective Future Vision. Canon can visualize the future she wants but she basically can only visualize a future where she is alive, so she basically has to keep reloading scenarios where she's alive to gather information. It's a power really only she could abuse both due to her pilot skill and her being an actual mechanic, so she basically was leap frogging on herself to speed up research development. The issue however was for a good portion of her run time, she was subconsciously sabotaging herself. Her subconscious was basically giving her coordinates for "Timelines where I have a chance to reunite with Kazuki on the island" rather than "Timelines where I finish development of the Einjahrhar" and only when she manages to reach her end goal and realize "I have an out" if she committed to that timeline pathway does she basically get her brain to commit to "I'm going to be making jumps to timelines where THE MOST people live."
tl;dr she had a search filter on for futures that required "I see Kazuki again on the island in the future" and that was fucking up her plan