I would combine highway and B-road ( secondary roads) mileage, alternating
between high and low rev engine use  and avoiding constant speed for
extended periods. I broke in the engine of my previous s Lexus doing
precisely that, and the engine really came into its own compared to other
cars of the same brand, which felt sluggish.
Also, short bursts of acceleration up to 100 mph , and cruising at variable
speeds  in the 50 to 85 mph range helped me loosen up the engine during the
first 4000 miles, plus, of course, some city driving. If you  do not want to
incur the wrath of the law by driving at 100 mph, downshift to 3d or 4th
speed , thus revving up the engine and achieving the same  effect .
Contrary to what manufacturers claim, break in periods are still required
for new cars.
Good luck.

I've taken 50 or 60 new cars and driven them for roughly 12,000 miles of
mostly highway driving with no problems.  The nature of our business was
most of the people in our office also had to drive mostly highway miles.
Figure 30 people get 4 new cars a year for 120 new cars a year, x my 15
years experience for 18,000 cars with no ill effects of driving mostly
highway miles from the time they are put into service.  Many of those cars
were bought by employees, relatives, and friends afterwards and they did not
experience any problems related to how the vehicles were broken in.

Enjoy your trip in your new ride!