As far as I know, "pickup" is a largely American term for "pickup" truck. Any other locations that use it probably import the same trucks and picked up the American usage. ...
I wouldn't expect any but U.S. dictionaries to include it.
The catch here is Canada. For the most part, Canadians use US slang, predominantly because of the amount of books, TV, film, and other pop-culture that makes it up here, but there is resistance to adopting US spelling and pronunciation.
While spelling is a bit of a mixed bag -- there are actual Canadian English dictionaries even though it isn't really thought of as a separate language -- a lot of slang words will use variant spellings from the US.
I would also use "pick-up truck", though some younger Canadians might not bother. The idea behind the spelling is that while "pickup" is being used as a single term, making "pick up" incorrect as it would imply an action, it would be grammatically incorrect to combine the two separate words into one word. Thus the hyphen is used as a concession to both theories: one term combining two words.
I suspect that many Brits would use the same spelling, for the same reasons. Brits would know the term "pickup truck" from films and TV, but would default to spelling it as "pick-up truck". In general, Britsh English still hyphentes many compound words which have become single words in American English: second-rate, part-time, take-off, well-known, low-level, etc.
This is changing, slowly, and even the Oxford dictionary has been listing an increasing number of words with the hyphen removed, but the Brtits have resisted the American tradition of hyphenless compounding.
Pickup, as in pickup truck, is one word. As to dictionaries, it was like that in the first one I checked: dictionary.com
If you scroll down the page about half-way, there's an entry from the Online Etymology Dictionary:
also pick-up, "that which is picked up," 1848; see pick up (v.). ...