Mr Boreland is believed to have survived a previous attack several years ago. The shooting has been condemned by senior politicians.
First Minister Arlene Foster said she was, “shocked and disgusted” and urged “everyone to work with the police as they investigate”.
Deputy First Minister Martin McGuinness said there could be “no justification for the murder of a well known loyalist in north Belfast”.
Who is John Boreland? Analysis – BBC News NI’s home affairs correspondent Vincent Kearney
He was quite a known figure and certainly for quite a number of years, he would have been quite a feared figure within north Belfast.
He was a leader of the UDA in the area and a close associate of two brothers, Andre and Ihab Shoukri.
In fact, he served time in prison after being convicted along with Andre Shoukri on a range of extortion charges.
The police at this stage say it’s too early to ascribe a definite motive but he did survive an attack two years ago which was believed to have been carried out by former associates of his within the UDA.
So this could be the result of an internal fight within the UDA because it has become so factionalised.
It could be a dispute between rival groups of UDA members or former UDA members.
However, because he was heavily involved in crime the police are saying, at this stage, that it’s possible this could have been a criminal motivation or it could be a combination of both – it could be UDA and criminal factors involved.
The DUP MLA Nelson McCausland said he had been at a church service in the area about an hour before the shooting.
“I want to express my sympathy to the family because no-one has the right to take life,” he said.
“We’ve had too many murders in north Belfast down through the years.
“These are things that should be of the past. We want to see guns off the street.”
Ulster Unionist councillor for the area David Browne condemned the shooting.
“My sympathies go to the family of the person who was shot,” he said.
BBC News NI’s Kevin Sharkey at the scene
There is a very heavy security force presence on the Ballysillan Road this morning.
There are a number of police vehicles which have sealed off part of the road immediately around Sunningdale Gardens.
People are already beginning to congregate, watching events as they begin to unfold.
John Boreland was heavily involved in criminality, he was a member of the UDA.
It appears as if this operation along the Ballysillan Road will continue for some time.
Feet away from me, there are heavily armed police officers, traffic is beginning to move along on this road.
ohn McBurney, a solicitor who served on a paramilitary disbandment panel, urged loyalist paramilitaries to “pull back from the precipice” in the wake of Mr Boreland’s murder.
He said that if the murder was motivated by “paramilitary, internecine warfare of some kind” then it was “exceedingly dangerous”