In regards to the canonicity of the game.
Straight from the mouth of the creator himself.
That said, I've just barely started reading the comics but I noticed an incongruity between the game and the comic. In the comic Hershel states that his son Shaun had been bitten before they had constructed the fence around the farm. He then died two days later before turning.
Yet in the game Shaun is reinforcing the already built fence and is killed on the spot by two walkers.
It's also a little odd at how advanced the decay is on the zombies at the beginning of the game. I know it's not explicitly stated but it seems that incident on the highway was at the very beginning of their rise and yet they're already portrayed as having decayed quite a bit.