How to handle a 9 hr layover in (potentially) both Toronto and Miami

Say potentially cause things might change over the next month with point bookings and all that but in the event this falls into place what is this boards thoughts on an extended layover in these two cities?

For Toronto: is a 9hr layover enough time to go see Niagra? Not necessarily do a full on tour/boat ride thing but see it and pictures and all that?

For miami: does going down ocean drive work or is getting a lunch in little Havana the better way to go?