I'm guessing the answer is:
We're found in vans, in bags, on bikes,
Postal vans, postmen carry bags and ride bikes, and all of these have letters
Most everywhere that people dwell.
And postal services are present in most populated areas
Dogs may hate us, but we bring
Dogs chasing postmen is a long-running trope
Important tidings, good or bad.
Letters carry news (e.g. in the past, news of a child being born, or a death)
We're found in books, in maps, online,
Letters of the alphabet
Most everywhere that info dwells.
A lot of information is written down with letters (most, because some information is pictorial)
China may hate us, but we're here:
Chinese writing uses logograms, which are pictorial representations of words (similar to Egyptian hieroglyphics); these are not letters
Edit - @Apep pointed out in the comments that this probably refers to China banning the letter 'N', which does fit the riddle much better.
Even in this riddle, you know.
Letters make up this riddle