Mike it is hard to tell them apart when they are not fruiting. I have never seen Rowan as a weed in Canberra so would ID this as Service Tree, which also tends to have blunt leaflets while those of Rowan tree tend to have more pointy or acute ends. Also the habitat in Scotland was to plant a Rowan tree in front of your house to ward of witches, so if you see a witch next to a Sorbus tree you know it must be Sorbus domestica and not S. aucuparia.