Definitely not from an argument, his costume alone shows premeditation as opposed to heat of the moment.

EDIT
So sorry Antimacy, didnt read your second post close enough there, thank you for that link!

EDIT
More info (I want to avoid Spam Posting)The locals seem to sharing what this was all about...
From the Toronto Sun
"Some residents, who didn’t want their names used, said the victim, whose first name is apparently “Johnny”, was well-known in Little Italy and may have had ties to organized crime.

They describe the shooting as a “public hit” by a Mafia hitman that was carried out on a day when most Italians were watching their national team play soccer in Little Italy.

“They (Mafia) wanted to send a message,” one man said. “They know everybody will be here watching the game.” "