What are the canonical definitions of vitarka-vicara in the Tripitaka or related literature
From Khuddaka Nikaya's The Questions of King Milinda (translation mine):


  ‘Venerable Nagasena, what is the characteristic mark of vitakka*?’ 
  
  ‘The characteristic mark of vitakka is "placing" (Appanā), Your Majesty.’  
  
  ‘Give me an example.’  
  
  ‘For example, Your Majesty, like a carpenter takes well-finished boards of wood and places (appeti) them in position.’    
  
  Mil 3.3.13


*ideation, reasoning, putting forward ideas, postulating a premise




  ‘Venerable Nagasena, what is the characteristic mark of vicāra*?’
  
  ‘The characteristic mark of vicāra is pondering/mulling over (anumajjana), Your Majesty.’
  
  ‘Give me an example.’
  
  ‘For example, Your Majesty, if you strike on a copper vessel, it then rings for a while, it responds with a sound. Here, Your Majesty, the strike is a simile for vitakka and the reverberation is a simile for vicāra.’
  
  Mil 3.3.14


*investigating a premise, considering an idea to weigh its implications