Turns out the Dodgers' "no signs or banners" policy applies to the Canadian flag as well.
According the Canadian sports website TheStar.com, security tried to confiscate the Canadian flag belonging to a Blue Jays fan because they felt it could cause fans to be aggressive toward each other. Needless to say, the Canadians in the section were furious, and several security guards and LAPD officers were called to the scene.
Well Canada, don't you worry. They weren't singling you out at all. We have had many an experience with confiscated banners.