Missouri because Blunt will run significantly behind Trump. Hillary's coattails could cost Rubio in Florida, but I suspect he'll run significantly ahead of Trump in the Cuban areas to narrowly win.
There needs to be another poll with Kander in the lead before I believe that he can unseat Blunt.
I have some theory that perhaps people who usually do not vote in Missouri are coming out for Trump, and their reasons for not turning out in the past was due to being dissatisfied with both parties, especially Democrats. However, they may be turning out to vote for Trump, and then vote for acceptable Democrats down ballot, such as Koster and Kander. Also, the similarities of the names may help Kander a slight bit.
Democrats should really go hard on Missouri.. it can get them a senate majority, and it is one of the very few media- red states that apparently can elect liberals statewide.
As far as Florida, I would not be too nervous about Rubio. Like you said, the Cuban vote should be quite heavy for Rubio. Plus he was an opponent of Trump in the primaries earlier this year, so he would not be as associated with Trump.
