30% of Canadians live in Ontario. About half of Ontarians live in the Toronto metro area alone. Overall about half the population lives in the top ten metro areas.
http://www12.statcan.ca/census-recensement/2006/as-sa/97-550...
A single rail line from Quebec City to Winnipeg, through Ottowa, Toronto, and Calgary, with a spur to Edmonton, would cover all eleven of Canada's largest cities, with 30% of its whole population. That's within those municipalities (i.e., people can take local transit to the inter-city rail line). You cannot draw any similar line that encompasses anywhere near that percentage of the U.S. population. Even if you connected America's 11 largest cities, you'd only have about 26 million people (about 8% of the country).
A big reason is that most people who live "in Dallas," for example, don't actually live in the city. Dallas and Ottawa are similar-sized cities of about a million people each. But Ottawa encompasses 70% of its metro area, while Dallas encompasses less than 20% of its metro area. Look at a satellite map of each city. Dallas is sprawl for about 40 miles in each direction from the city center. 40 miles from Ottawa is nothing in every direction (and for the most part, so is 20 miles).
The obvious question is how many infrastructure hubs (cell towers, train stations, highways, etc.) are needed to cover X% of the population. And following that, how closely connected those hubs would be.
Suggestions like "Canadians live near the border, but Americans live near the coast so it's similar" completely ignore that reality. The Acela corridor (D.C. to Boston, including Philadelphia and NYC) is the most efficient population-coverage route I know of in the country, but it can't possibly touch the efficiency of that Quebec City to Winnipeg line. Among other things, America has two coasts, and also vastly less urban density than Canada.
I can't speak for the latter, but we took the Canadian from Vancouver-Winnipeg for a family reunion a few years back. It was a great trip, except for the 6h delay sitting just outside Winnipeg due to backed up freight traffic (I believe VIA leases access to most of the track, and has to yield to any freight trains) that meant we were getting off the train and had to find a hotel at midnight, instead of getting picked up by family at a reasonable hour.
I'm saying that the raw number isn't meaningful, and you have to zoom in to find value and evaluate it in context.