Omar Sy is 6'3", Hart is 5'4"... that's a foot difference and I'm sure Cranston is bigger than Hart.
In the original movie the point of Omar Sy helping out the other characters who is a quadriplegic is that he's a large man and can help the man he's caring for get to the toilet/bathtub/bed, etc. Why would Bryan Cranston hire tiny Kevin Hart as a caregiver?