Canned Salmon is too high in sodium for me, so I use generic frozen salmon instead -- reduces sodium portion from salmon from 285 to 40, a big change. Once the fish is thawed, I don't dice it, but shred it by hand in to little bits. Also, lower the bread crumbs as others have suggested to 3/4 cup -- a far better salmon/bread ratio.
Instead of Dijon mustard, I like the impact of spicy brown mustard instead. I once used "Mae Ploy" Thai Sweet Chili Sauce instead of the mustard, and that was a huge hit. If you go that route, nix the dill sauce and go with a tomato/pepper sauce instead. Awesome.
Also, I don't have the patience to dice the onion, so i use a coarse cheese grater and shred them. It doesn't work too well with celery, but the onion is very fine and mixes very well.