Is Canada underpopulated?

Neil Reynolds thinks it is, and he may have a point. Neil's column today in the Globe and Mail is titled "Go forth, multiply and fill the provinces." This will make environmental activists pull their hair out. Can you see David Suzuki pulling his hair out?
If you have ever traveled across this vast country as I have, you have to be struck by it's emptiness compared to traveling in Europe for example. We have very few large metropolitan areas outside of Toronto and Montreal (maybe Vancouver), most of the cities are relatively small with big spaces in between. Population density in Canada is around 3.3 people per square kilometre, yet most of it is closer to zero. Our replacement birth rate is well under 2.1, which means we are not going to grow unless we have a huge influx of immigration.
In Brian Lee Crowley's recent book Fearful Symmetry he mentions exactly that idea, and that many entitlement programs cannot be maintained as well as labour shortages looming in Canada's future unless the birth rate changes dramatically.
Of course this is true in much of Europe; Japan's population is already shrinking, and wait until the Chinese figure out that their one-child policy could hurt them. America has one of the highest birth rates in the industrialized world, but it too is below 2.1. This issue will give policy-wonks in the industrialized world grey hair.