In a large pot, melt butter over medium heat. If using the Canadian bacon, cook it first and eliminate the butter and saute the following in the bacon fat.
Saute celery, onion, bay leaf, dill, 1/2 tsp salt and 1/4 tsp pepper for about 5 min or until onions start to brown.
Stir in potatoes; saute for 2 min.
Increase heat to medium-high; stir in water and bring to a boil. Cover, reduce heat to medium and boil for about 5 min or until potatoes are almost tender.
Whisk flour into milk and stir into pot; bring to a simmer, stirring often.
Stir in fish or seafood; simmer, stirring often for 5 min or until fish is opaque and flakes easily with a fork or seafood is hot.
Discard bay leaf.
Stir in lemon juice and season to taste with salt and pepper. Ladle into bowls and top each serving with crumbled crackers.