The Trans-Canada Highway is in Canada.
Canada is the second largest country in the world, and the largest country that it is easy to travel across. The Trans-Canada Highway connects all ten provinces and is 8030 km (just under 5000 miles) long. Most Canadians have some interest in seeing the entire country and driving across Canada is a common way of doing it. Note that there is more than one highway that spans the entire country including:
 Get in
This trip can be started anywhere in Canada. Technically the Highway runs from Victoria (British Columbia) to St. John's, Newfoundland (or the other way around, both cities declare a "mile 0" for the highway). However, for practical purposes many travellers skip the trip to Newfoundland, and end it in Halifax, others may skip Victoria and end it in Vancouver.
The trip will be detailed from west to east, obviously it could be done in the reverse direction. There are some locations where multiple routes are called the Trans-Canada highway. Generally the routes that go through the larger cities will be the route taken.
The highway, designated as Highway 1 in the four western provinces goes through the magnificent mountains of British Columbia and western Alberta and the awe inspiring prairies of Alberta, Saskatchewan and Manitoba.
That route more-or-less follows the Canadian Pacific Railway line. An alternative would be to follow the Canadian National line. The route would be the same up to Kamloops, but would then swing further North:
 Winnipeg to Ottawa
The Trans Canada runs over prairie for a little way East of Winnipeg, then a long stretch (2000 km?) of lightly inhabited forested country. It is called Highway 17 most of the way across Ontario, and 417 near Ottawa. Towns on the route are:
From Thunder Bay to the Sault, the road winds along the shore of Lake Superior and is quite pretty.
An alternate route further North is Highway 11, Thunder Bay via Kapuskasing to North Bay.
 Ottawa to Moncton
 Moncton to North Sydney
 Prince Edward Island
The Trans-Canada Highway crosses the Norththumberland Strait by the way of the 9 km Confederation Bridge and the Wood Islands ferry crossing. Depending the direction you come from, if you land on the island using the bridge, the TCH starts in Borden and meanders across the southern part of Queens County towards the City of Charlottetown. Charlottetown lies about the halfway point. Leaving Charlottetown it crosses into Kings County ending at the ferry terminal in Wood Islands. Along the way are many beautiful scenes and lots to do in Charlottetown. This is the shortest TCH section within any provincial border. The time to drive from Borden to Wood Islands, if you don't stop along the way, is approximately 95 minutes. All worth it because you'll be tempted to explore off the TCH as PEI has some of the most beautiful countryside anywhere.
 Nova Scotia
 Port aux Basques to St. John's
 Stay safe
The weather in parts of Canada can be pretty extreme in the winter, so this trip is best done in the spring, summer or early fall.