St. Paul to Dawson Creek

Since the exchange rate is what it is, it would be cheaper on gas prices also.

I agree with ROMORE. have done that route (in reverse) and believe it to be the best choice for you.

The most direct route would through Grand Forks to Winnipeg then west. At Portage La Prairie take 16 (Yellowhead) to just west of Edmonton and highway 43 to Grande Prairie and 2 to DC.
25 hours sounds about right, I made that trip from Prince George. It's a long drive without a lot of scenery.

There are 3 main border crossings for you to choose from

I29 Grand Forks to Winnipeg

US52 Portal in western North Dakota

I15 Sweetgrass in Montana

Google Maps gives time estimates of 26, 25, 27 hrs respectively, times roughly matching the distances. I was going to say the average highway speeds on the Montana route would be faster due to more freeway - but the shortest way from I94 in the east to I15 at Great Falls is MT200.

The total time will depend more on how long you spend at the overnight stops, than on the actual driving distance and time.

We crossed at Sweetgrass (Montana) and drove thru Alberta, Calgary, Edmonton, and Grand Prairie on our way to Dawson Creek. We did not have any trouble going thru the Calgary/Edmonton areas but we did make a wrong turn in Grand Prairie due to construction but had no trouble getting back on course. We found the roads around Grand Prarie had lots of dips in them with a high speed limit so you may want to watch it in that area.

Head NW thru Montana, cross the border toward Edmonton and keep going.