Slang in Canada. Origin unknown. Possibly started in New England, and made it's way up and then to the west coast. Likely derived from 'do-gooder'. Sounds like an Aussie thing to me.
1. good time/night/day 2. job well done
3. something particularly funny
1. Talk to you later, have a gooder!
2. Dankblunt, m8. A right gooder that one was
3. The new iDubbbz video was a real gooder