Four thoughts...
A. It really is impossible to recommend leaving behind any of those lenses as it is highly dependent on your personal vision and shooting style. Go back over the landscapes you've shot in the past; Lightroom has a great Find module for that. What are you using the most?
B. I've been twice to Iceland - June and March. I've shot compelling landscapes from 18mm to 400mm. The only recommendation I would make would be to take two of the Leica lenses in carry-on with the body, and the other two in checked luggage. If your checking it all then take all.
C. If you're shooting professionally, then I think you would want all four of the Leica lenses. If not, then leave one system behind as even the Canon would cover all your needs if it's fairly recent with a good range of focal lengths. If jt's not wide enough, you can always stitch.
D. Have a look at my Flickr
Iceland 2017 and
Iceland 2016 albums as it will tell you which focal lengths were used for each photo. Although they were shot with an RX10iii, a 35mm equivalent focal length is provided. I typically shoot wide (18-28mm), but many landscapes in Iceland are at longer focal lengths because of the open, clear vistas, long distances and beautiful receding mountains.