The 144th goal of her illustrious career came on a penalty shot in the 37th minute.
"It felt incredible to be back out there," Sinclair said. "I put the penalty bottom left, keeper guessed the right way — but it beat her."
Sinclair hadn't played since Canada's bronze-medal victory over France at the London Olympics. She was suspended for an incident following Canada's 4-3 extra-time loss to the United States in the semifinals at the London Olympics.
Sinclair, who recorded a hat trick in that loss to the Americans, finished her suspension Wednesday in Canada's 2-0 win over Switzerland in its Cyprus Cup opener.
Jonelle Filigno scored Canada's first goal in the 30th minute Friday, taking a pass from Sophie Schmidt and blasting a hard shot to the top corner from 18 yards out.
"I was happy with the overall performance," Canada's coach John Herdman said. "Thankfully Sinclair and Filigno scored the goals to take us to the final."
Emmi Alanen had scored in the sixth minute to give Finland an early lead, collecting a loose ball and beating Canadian goalkeeper Karina LeBlanc from inside the area.
Canada will finish group play against the Netherlands on Monday, and then meet either England or New Zealand in Wednesday's final.