Tuesday's trade could open regular playing time for Blue Jays outfielder Anthony Alford, one of Toronto's top prospects. Alford was recalled from Triple-A Buffalo on Tuesday.
Pillar, 30, has spent his entire major league career with the Blue Jays, batting .260 in seven seasons. He is 1-for-16 in his first five games this season.
Pillar has 55 home runs and 231 RBIs in 695 games. He's known for his highlight-reel catches in center and was Toronto's longest-tenured player.
The Blue Jays shared a message from Pillar to their fans on Twitter.
The right-handed-hitting Pillar figures to see regular playing time in San Francisco's outfield. Left-handed Steven Duggar has started in center field in each of the Giants' first five games this season.
Hanson is a career .238 hitter with 12 home runs and 51 RBIs in 243 games for Pittsburgh, the White Sox and San Francisco. Law is 9-3 with five saves and a 3.83 ERA in 109 games over three seasons with the Giants. De Paula struck out 55 batters in 52 ⅓ innings in Class-A last season.
The Giants designated outfielder Michael Reed for assignment to make room for Pillar on the roster.
The Associated Press contributed to this report.