The US has never won the Rugby World Cup.
World cup for fifa is enteirly different to Rugby. So the answer is ZERO.
once in rugby sevens
In spite of having qualified for all seven Rugby World Cup tournaments to date, Romania have never won the Rugby World Cup.
New Zealand joint-hosted the 1987 Rugby World Cup, as well as hosting the 2011 Rugby World Cup in their own right.
all six times
twice at time of answering(2012) 1991 and 1999
Scotland have competed in all 7 Rugby World Cups to date. They were in 1987, 1991, 1995, 1999, 2003, 2007 and 2011. They will compete in the 2015 Rugby World Cup too.
to 2015 they have never won
I doubt if Canada have won it ever.
Twice. In 1987 and in 2011.
They have won in 0 times since their first appearance in the world cup in 1987. The furthest they have reached is the quarter finals.