I do either ground beef with some onion and garlic and then stuff that after cooking and top with just a plain old tomato sauce and mozzarella sprinkled over all...OR...shred cooked chicken breast, add in a bunch of grated mozzarella and some cooked, squeezed dry spinach and an egg. That works well with a tomato basil sauce. Mmmmmm. Envying you. I haven't made cannelloni in ages.
You're only given a little spark of madness. You mustn't lose it. Robin Williams Alix
For the filling I would do ground beef/pork or a combo of the two, sauteed onion, fresh parsley, some garlic, a little nutmeg, then fold in ricotta, shredded mozz, and grated parm. Just to where it is pipeable then fill tubes. layer in pan, cover in a good tomato sauce, more cheese and bake.