Their situation is very different in terms of demography. The U.S. has a fertility rate of 2.1%, so the level of fertility in the U.S. is high enough to replace the generation. Their population is younger than the Canadian population. The baby boomers were also an important factor in the U.S., as in Canada, but I think following the baby boom, their fertility hasn't dropped as low as ours.
On June 13th, 2006. See this statement in context.