Police seized £200,000 worth of suspected herbal cannabis after a car was stopped on the M2 motorway around 12:00 GMT on Friday.
Properties were searched at Shore Road, Belfast, and in Newtownards, County Down, as part of the investigation.
A further £200,000 worth of suspected herbal cannabis was seized in Antrim.
Police said both seizures were "being investigated to establish the existence of any links".
A man and a woman in their 30s have been arrested following the seizure of £400,000 worth of suspected herbal cannabis.