Pretty sure the route is about as direct as it can get given the terrain.
That said, if BC could build the Coquahalla 25 years ago and it can be driven at 120 end to end, there is no reason why that can't be done for the rest of the #1. That said, the #5 would be easier to twin, despite it's lower usage. Maybe it'd be used more if it was twinned and 120kph instead of single lane and 80-100.
We really do need a national freeway system that links all the major cities, economically important centres, and minor territorial/provincial centres. Build it to be driven at 120kph; provinces can opt for a higher design limit if they wish, but they have to contribute the extra costs of construction and maintenance. Set it up so that the speed limit varies based on road conditions.
I'm not sure which Highways I'd nominate for the system out east. Out west I'd nominate Hwy 1 from Horseshoe Bay to Hope, as well as Highway 17 from Tsawwassen to the Hwy 1 interchange. From Hope, #5 to Kamloops, and then along the #1 again all the way to the Ontario Border. I'd also suggest the 97 all the way up through Prince George and Whitehorse to Alaska, and the 16 along it's whole length from Prince Rupert to the Hwy 1 interchange west of Winnipeg. Other Highways to consider to make it networked would be the #5 from Kamloops to the #16 interchange near Valemount, Hwy 4 from the Montana border to Lethbridge, Hwy 3 from Lethbridge to the Hwy 2 interchange near Fort Macleod, and Hwy 2 all the way up to Edmonton. A route from Edmonton to Yellowknife. A route from Yellowknife to Whitehorse. A route from Saskatoon to Regina to the American border through Estevan, and a route from Churchill to Winnipeg to the American border.
I get that a number of these would be impractical. But I believe that the only way to truly open up the north to economic growth in a beneficial way to the nation is to make it more accessible and more practical to live there. This will encourage more people to settle up there, make products for people already living up there cheaper, and god forbid should we end up fighting over the arctic the logistical infrastructure would be in place for ground deployment and supplying of military assets.