1. a-More people are visiting museums in US than in Canada
b-More people are visiting museums in US than the ones in Canada
The both is OK and sounds fine to me. Maybe the first one emphasizes the country while the latter does it for the museums in Canada. We'd better wait for a native-speaker to pay a visit to this thread whether the both sentences do differ in the aspect they are referring to or they don't
2. With her command of pathos and tragedy and being humorous, George Eliot is considered to be a great English novelist.
It sounds good to me.I see nothing wrong
3. The labor union is negotiating a contract with the hospital that will satisfy the demands of the workers and be acceptable to all levels of management.
Yes,there should be "will" because it is about an action which will occur in the future (I mean the result of the negotiation will be declared to the concerning parties to see whether it will be both satisfying for the workers and acceptable for the management)