Q:

Looking for a film where the demon whistles

I am trying to find a film that I saw about 10 years ago (maybe a little less than that). 
I thought Wesley Snipes was the main character, but I checked IMDB and couldn't find it in his filmography :/
Here are the things I remember:

It was made some time in the 90s or possibly early 00's
There is a demon that uses people as a host, so it randomly jumps from one body to another
The person that the demon jumps into always whistles a tune
I THINK the main character was a cop
It's American

 I remember at the ending of the film the main character and the demon (who is in the main characters friend or partner) are at a cabin or some other place in the woods and there is a confrontation. 

Can anyone help me with this film please? 

A:

You are looking for Fallen (1998)

The demon is played by various actors most memorable of which is John Goodman in the final confrontation at the cabin where he behaves exactly as you describe.  He portrays a sadistic demon that keeps whistling 'Time is on my Side' while jumping from person to person and performing murders and suicides. 
The American detective you describe is played by Denzel Washington. 
Here's the trailer on YouTube.