“If you own 2 or more houses can you grow more than 4 plants?”
Federal law, within the Cannabis Act, states the limitations on the number of plants that can be cultivated and possessed by individuals; the NB Cannabis Control Act has not restricted it further, thus it is the federal law that should form the answer here.
There are two different ways this is discussed:
1) "it is prohibited for an individual who is 18 years of age or older to cultivate, propagate or harvest...more than four cannabis plants at any one time in their dwelling-house", while this states the maximum in one dwelling-house it does not speak to multiple houses; and,
2) more broadly, under section 8 it is stated "Unless authorized under this Act, it is prohibited...for an individual to possess more than four cannabis plants that are not budding or flowering".
This is something that, if you have any question, you should seek legal counsel when planning your own activities and purposes for cultivation, to get more specific advice for your circumstances. However, from the Cannabis Act, it does appear as though the limit is just the 4 plants maximum.