From Tad Friend’s “California Postcard: Pot 101″ piece in the New Yorker‘s Talk of the Town section, 8/9/10:
The university’s [Oaksterdam University in Oakland CA, which "aims to reposition pot-smoking as both a civil right and as the stuff of empire"] founder, president, and horticulture professor is Richard Lee, who also owns seven local enterprises that have helped revitalize the once derelict neighborhood, five of them so-called “canna-businesses.” (p. 22)
This is an overlap portmanteau, in fact a telescoping: cannabis business > canna-business, with the -bis of cannabis truncated by the overlap with business.
Respectable number of ghits, with all three spellings (solid cannabusiness, hyphenated canna-business, separated canna business) represented in the mix. Here, for example, you can find Stoner Magazine (U.K.) — “Your Cannabis Culture Magazine” — with its Canna Business Directory (listing head/hydroponic shops in England and Scotland, but not Wales or Northern Ireland, plus the Netherlands and Switzerland).
[Though you might not see this right away, head shop is an ordinary (type O) N+N compound, when understood as 'shop for heads', with modifying N head 'pothead, person who enjoys marijuana'. Hydroponic shop, however, is a type X Adj+N composite, since the Adj hydroponic in it is non-predicating, but is instead interpreted via the plural N hydroponics 'equipment for growing plants hydroponically').]