Miah-Marie Langlois added 11, while Lizanne Murphy finished with 10 for the Canadians, who led by just three points going into the fourth quarter.
Canada pulled away down the stretch, and when Tatham scored on a three-pointer with 1:12 to play, it brought the crowd to its feet and gave the Canadians a 14-point lead.
For the second straight night, the Canadians enjoyed a noisy, near-capacity crowd at Ryerson University's Mattamy Athletic Centre — formerly Maple Leaf Gardens.
Indiana Fever rookie Natalie Achonwa made her first appearance with Canada's team since tearing her ACL in her what would be her final game with Notre Dame in the spring of 2014. Achonwa checked in with 5:30 to go in the first quarter, and made an immediate impact, cutting hard to the basket and drawing a shooting foul.
Achonwa would finish with five points in just over 10 minutes as coach Lisa Thomaidis works her back into the rotation.
Canada, which demolished Venezuela 101-38 in its opener Thursday night, is playing its first meaningful event on home turf since the FIBA Americas tournament in Hamilton, Ont., in 1995. It tips off a big summer for the Canadian women, who open the FIBA Americas Olympic qualifying tournament on Aug. 9 in Edmonton.
Argentina, meanwhile, dropped a 68-55 decision to Cuba in its opener.
Canada raced out to a 19-6 lead and looked en route to another easy victory, but Argentina had pulled to within 28-21 at halftime.
The Argentines opened the third quarter with a 12-2 run and pulled even at 35-35 with six minutes to play.
Canada took a 47-44 lead into the fourth quarter.
The Canadians face Cuba on Saturday night. The semifinals are Sunday, and the medal games are scheduled for Monday before the men's tournament gets underway Tuesday.
Canada has never won the Pan Am basketball tournament, but the women have one silver and three bronze in 14 Pan Ams.