spaceyjase "rtfm" is a bit rude. Anyways, CanvasLayer doesn't inherit from Control, and does not have the mouse_filter property. It's possible that one of its descendants has mouse_filter set to MOUSE_FILTER_STOP and is eating the event, or it could be something else.
@Hexxxen See if that fix works. Both PASS and IGNORE are fine on a Control you don't want blocking clicks. If that isn't the issue, can you share your unit selection code?