Sight unseen (I'm going to a Nikon Z launch event tomorrow, and will also attend a local Canon R event when I hear of one), I far prefer the Nikon for my needs (landscape, often on long backcountry hikes)...
1.) D850 sensor vs. 5DmkIV sensor. For me, the whole point of full-frame is image quality that nothing less can bring - I shoot 24 MP APS-C Fuji, and would only consider something that can really beat that. Canon offers a barely noticeable 6 extra MP, and about 2/3 of a stop of extra DR - mostly by setting the (indicated - I know that what Fuji considers 200 is more like 125 to Canon or Nikon) ISO below Fuji's 200 minimum. Nikon offers nearly double the pixels I have, and something close to 1.5 stops of extra DR (by using ISO 64).
2.) Lenses. This is tricky, because it requires assumptions on optical quality. Everybody who's shot with the Nikon says the lenses are great, but that is still in the "remains to be seen" category. I like the size and weight of the initial Nikon lenses much better. Two of Canon's four are so heavy I would never consider them, and there's no roadmap to see what's coming. Nikon has a 24-70 that I consider a near-perfect backpacking lens (Canon's 24-105 is a little big, but acceptable), and a roadmap that shows a reasonable-size 14-30 on its way. If those Nikkors live up to the claimed quality, it's a darned nice start.
3.)IBIS. Nikon yes, Canon no...
4.)Weather sealing. Nikon specifically says D850 level, which is a very small step down from their best (D5), and is built to survive the backcountry. Canon says (insert sound of crickets) "it has some sealing". My guess is 6D/80D type sealing, which is similar to the D610 and a little better than the Sonys. If it had their best or something close, I'd hope they'd say it. Maybe it does, and that'll come out soon?The latest Fujis are similar to a D850, and I don't want to go down a level...
5.) Cards. I don't love one card slot on either camera, but Nikon's is XQD with improved speed and durability. At this level, I'm not concerned with replacing a few hundred dollars worth of memory cards. That would be a real consideration on a sub-$1000 camera.