What are the three marks of existence? What are the three marks of existence and where are they found in the canon? Is there any fundamental differences in interpretation among the different traditions?
The Three characteristics of existence are part of the core teaching of the Buddha and found throughout his teachings. In essence every single compound (i.e. made of the 5 aggregates and/or the four elements) thing has these characteristics inherent in their very existence. 

When one realizes with their own experiential knowledge that all things we have attachments and aversions to have at their core these three characteristics, then there is nothing to cling to, nothing to run from, there is just peace.

We understand that everything, from the universe itself down to ourselves and our loved ones are subject to change and decay(impermanence). We understand that every compound thing is subject to and can be part of the cause of Dukkha(unsatisfactoriness/suffering). Because of our attachments and aversions, nothing created can bring lasting happiness. And Thirdly we understand that there can be found nothing that we can truly identify as "self". What we take to be self is not-self. There is no inherent permanent self/identity in anything created, the "self" we take to be us is merely a coming together of the 5 aggregates (form, feeling, perception, mental formations, consciousness), processes that come into being, and eventually decay.

As far as I know( and I'd love to be proven wrong on this if anyone can link it) there is no one grand sutta solely on this specific topic, but it is inherently at the core of all of the teachings and therefore pervades the whole cannon. I agree with what Catpnosis said about there being no fundamental differences, but differences in interpretation and usage as part of the various paths.

Here are a few Suttas regarding the three characteristics:


  Dhamma-niyama Sutta: The Discourse on the Orderliness of the Dhamma
  
  "Monks, whether or not there is the arising of Tathagatas, this property stands — this steadfastness of the Dhamma, this orderliness of the Dhamma: All processes are inconstant.
  
  "Whether or not there is the arising of Tathagatas, this property stands — this steadfastness of the Dhamma, this orderliness of the Dhamma: All processes are stressful.
  
  "Whether or not there is the arising of Tathagatas, this property stands — this steadfastness of the Dhamma, this orderliness of the Dhamma: All phenomena are not-self.


And from the Dhammapada:


  Maggavagga: The Path
  
  
  "All conditioned things are impermanent" — when one sees this with wisdom, one turns away from suffering. This is the path to purification.
  "All conditioned things are unsatisfactory" — when one sees this with wisdom, one turns away from suffering. This is the path to purification.
  "All things are not-self" — when one sees this with wisdom, one turns away from suffering. This is the path to purification.
  


I think this passage from the Maha-parinibbana Sutta speaks volumes about understanding impermanence:


  
  Then, when the Blessed One had passed away, some bhikkhus, not yet freed from passion, lifted up their arms and wept; and some, flinging themselves on the ground, rolled from side to side and wept, lamenting: "Too soon has the Blessed One come to his Parinibbana! Too soon has the Happy One come to his Parinibbana! Too soon has the Eye of the World vanished from sight!"
  
  
  But the bhikkhus who were freed from passion, mindful and clearly comprehending, reflected in this way: "Impermanent are all compounded things. How could this be otherwise?"


Of course Dukkha is all over the teachings.. heck it's the first noble truth:


  "Now this, monks, is the Noble Truth of dukkha: Birth is dukkha, aging is dukkha, death is dukkha; sorrow, lamentation, pain, grief, &amp; despair are dukkha; association with the unbeloved is dukkha; separation from the loved is dukkha; not getting what is wanted is dukkha. In short, the five clinging-aggregates are dukkha."


And about not-self:


  Anatta-lakkhana Sutta: The Discourse on the Not-self Characteristic
  
  "Bhikkhus, form is not-self. Were form self, then this form would not lead to affliction, and one could have it of form: 'Let my form be thus, let my form be not thus.' And since form is not-self, so it leads to affliction, and none can have it of form: 'Let my form be thus, let my form be not thus.'
  
  "Bhikkhus, feeling is not-self...
  
  "Bhikkhus, perception is not-self...
  
  "Bhikkhus, determinations are not-self...
  
  "Bhikkhus, consciousness is not self. Were consciousness self, then this consciousness would not lead to affliction, and one could have it of consciousness: 'Let my consciousness be thus, let my consciousness be not thus.' And since consciousness is not-self, so it leads to affliction, and none can have it of consciousness: 'Let my consciousness be thus, let my consciousness be not thus.'