What kind of fish is this (Florida, USA)?
So after much more time on this than I should have, I am pretty confident this is a silver jenny (Mojarra). 

Silver Jenny, Eucinostomus gula


  "The Silver Jenny, Eucinostomus gula, whose common Spanish name is
  mojarra Española, is a species in the Mojarra or Gerreidae Family,
  known collectively as mojarras in Mexico. Globally, there are eleven
  species in the genus Eucinostomus, all of which are found in Mexican
  waters, seven in the Atlantic and four in the Pacific."


Dorsal fin structure, tail fin split, location of ventral fins and gill fins all match up, as does color.  So does the faint stripe from top of gill to back of fish. The last clue was the protrusible mouth.

I'm surprised you found it in a canal, as it is a saltwater fish. Were you close to the ocean?  From the link above:


  The Silver Jenny are an abundant schooling species that are found
  seasonally in shallow coastal waters over mud bottoms in mangrove
  lined lagoons and creeks in waters that are between 11oC (52oF) and
  28oC (82oF) at depths up to 175 feet. Juveniles are found in seagrass
  beds. They may also enter freshwater. They are known to make seasonal
  migrations to off-shore warmer waters during the cooler months for
  wintering and hibernation returning to coastal waters in the spring
  for breeding. They reach a maximum length of 23 cm (9.1 inches). They
  are benthic feeders that probe the bottom with their protrusible mouth
  consuming bivalves, crustaceans, ostracods and detritus. They are a
  poorly studied species and very limited information is available about
  their behavioral patterns.




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