UNB will play No. 1 Alberta in Sunday's final after the defending champion Golden Bears downed the University of Quebec at Trois-Rivieres 5-1 in the other semifinal game Saturday. Guelph plays UQTR for bronze.
Halley completed the hat trick with 65 seconds left in the third period. He added an empty-netter 28 seconds later to seal the win.
He said linemates Dana Fraser and Philippe Maillet deserved credit for giving him scoring opportunities.
"They were great at finding me on the ice and I just had to put the puck in the net," Halley said.
Cam Braes had the other goal for the Varsity Reds. UNB outshot Guelph 40-15.
"We pride ourselves on our third periods and we got better throughout the game," said UNB defenceman Adrian Robertson.
Nicholas Trecapelli and Nicklas Huard scored for the Gryphons.
Jordan Hickmott scored twice, including an empty-net goal at 19:00 of the third period, and added an assist as Alberta topped the Patriotes in the later semi.
Brett Ferguson and Kruise Reddick had a goal and an assist apiece and Koper Levko also scored for the Golden Bears.
"It has been our goal from Day 1," Reddick said when asked about having the opportunity to defend their championship. "Not only for ourselves as individuals, but also for our program and its great history."
The Golden Bears program will be playing for its 15th Canadian university title.
Tommy Tremblay replied with a power-play goal for UQTR.
Luke Siemens made 16 saves in the win. Guillaume Nadeau stopped 37-of-41 shots in the losing effort.