See Spot Run (2001)

Gordon Smith is an offbeat mailman who has never met a dog he couldn't handle. When he offers to baby-sit James, the young son of his beautiful neighbor Stephanie, he hopes to spark her romantic interest in him. A hard working single mom, Stephanie thinks Gordon is just an overgrown kid himself, but circumstances force her to leave James with him, temporarily, while she is away on business. Meanwhile, FBI Agent Murdoch is trying desperately to find his runaway canine partner, Agent 11, who has escaped from protective custody. Thanks to the super dog's drug detecting abilities, he has incurred the wrath of local mobster kingpin Sonny Talia, who has put out a contract on the four-footed Fed. They lose the trail completely when the dog seeks refuge in Gordon's mail truck, where he is promptly adopted by James, who names him "Spot." While Stephanie tries desperately to return home in the midst of a snowstorm, the fur begins to fly as the mobsters catch up with Gordon and James at a local pet store...