See Spot Run (2001)

Synopsis
A police dog finds himself pitted in a battle of wits against an accident-prone mailman and a gang of crooks (and it looks like the dog has the edge in the brains department) in this broad comedy. Agent 11 (Bob) is a bulldog trained by the FBI agent Murdoch (Michael Clarke Duncan) to sniff out drugs, and the dog's keen nose ferrets out the storage facility of Mafia kingpin Sonny (Paul Sorvino); Agent 11 has also been taught to show no mercy with criminals, and he gives Sonny a serious bite in a rather personal place. Needless to say, Sonny is not amused, and wants revenge against the pooch, so Agent 11 is put into the animal equivalent of the witness protection program. However, unlikely circumstances set the dog loose, where he soon pairs up with Gordon (David Arquette), a stunningly inept letter carrier with a long history of fending off ill-tempered pets. Gordon is attempting to impress Stephanie (Leslie Bibb), an attractive single mother, by helping to look after her son James (Angus T. Jones), and when he comes across Agent 11, he adopts the dog and names him Spot, feeling certain he can smooth out the critter's often cranky relationship with people. But Gordon doesn't know that Sonny and his henchmen are hot on Agent 11's trail and that his new best friend will lead a gang of ruthless gangsters into Stephanie and James' home. See Spot Run was originally announced as a vehicle for comedy star Martin Lawrence, but when changes in Lawrence's schedule prevented him from taking on the project, it was retooled for the talents of David Arquette. ~ Mark Deming, All Movie Guide