Coast to Coast? Sure, but every city in North America? Nah, that isn’t practical at all.
For instance France apparently builds high speed rail for 25 Million per kilometer so lets use their cost number. The straightline distance, shortest possible, from Denver to Omaha is 483 kilometers so the line from Omaha to Denver alone would cost 12 BILLION dollars.
Denver to Salt Lake is 590 Kilometers, again straight line, so there goes another 14.7 Billion dollars. (This is also absolutely impossible to do at this price) SLC to Los Angeles is 930 kilometers, another 23.2 Billion.
We’ve now spent 49.9 Billion to connect just FOUR cities and only have a single rail line that goes from Omaha to LA. If you want coast to coast then a single least possible distance link from D.C. to San Francisco would cost right at $100 Billion.
All of those calculations assume the 25 Million per kilometer can be done in the United States too. For example the High Speed rail being built in California is costing four times as much.
So no, trying to connect every city in North America with High Speed rail not only isn’t practical it isn’t economically possible on any reasonable timeline as it would require a major percentage of the US’s entire GDP to be spent on it every single year for the next century. The US is fucking huge and we have a lot of cities.