He died of an aneurisym.
http://www.thestar.com/article/173096
and
http://www.thestar.com/article/173465
from The Toronto Star:
DOHERTY, Dennis
DOHERTY, Dennis Died Friday, January 19, 2007, at his home in Mississauga, after complications from surgery. His father was a plumber, but he had bad pipes. He's off to meet his late wife Jeanette and will be missed by his devoted children Emberly, John and Jessica, his brother Joseph, sisters Franny, Guzzie and Dee Dee, all his extended family and those who loved his music. Visitation will be held at the funeral home of Skinner & Middlebrook Ltd., 128 Lakeshore Rd. E. (one block west of Hurontario St.), Mississauga on Tuesday, January 23, 2007 from 3-7 p.m. Interment will take place in Nova Scotia. An entertainer right to the end. Love You Pops.