Nick Cannon -- Buying Dem Babies 3 MIL Worth Of Crawl Space

Nick Cannon is becoming a bridge and tunnel kind of guy ... moving to New Jersey where the twins will have 2 lush acres in which to roam.

We're told Nick strategically picked Saddle River -- 1 hour out of NYC -- to keep the 3-year-olds out of the spotlight. Fact is ... it would be hard to find the equivalent in the City. The house has 6 bedrooms, 8 baths, a private lake, and on and on.

Nick's renting to own, but not because he can't cut it. He'll pay $11k a month with an option to buy the $3 mil estate, assuming he likes it enough.

The house will not have Mariah's ornate touches. Nick's mom will help him decorate ... after his escapades a few weeks back, we're guessing there might be some Jamaican influences.