being a french film maker the odds are that the driver was also french(big time national pride thing over there), so i am trying to think of what young jet setters would have been french and in F1 back then to hang out with a film maker and make such a movie.
the number of french drivers in F1 was pretty slim in the late 70's and early 80's, much less the ones brash enough to do something like this on public roads.
possible suspects:
Patrick Depailler was a very good driver, won a few GP during his career including Monte Carlo in 1978 before passing away shortly after the British GP in 1980.
Jacques Laffite was an excellant driver and had a fairly long F1 career. he won 6 GP and was actually born in Paris just as the filmmaker in question did. he certainly had a rebel streak in him from some of the stories i read, which makes him a good candidate to do something like this. he was talented enough to continue driving all the way up to 1986
Jean Pierre Jabouille was around at the time. good driver, won a few GP. but stories i can find of his life/career don't lead me to believe he was enough of a wild man to attack a public road like this.
Jean Pierre Jarier was a serviceable driver. always played second chair to bigger names though. he was well past his prime in 1978, peaking in 1975 scoring points 5 times, sitting on a few poles, and setting a few fastest laps. never won a GP.
René Arnoux won 7 GP in his career, but i can't really find much else on him in a quick search. i doubt a task like this would end up in the hands of someone who wasn't flashy or out for a thrill, but it is possible that a driver in his early 30's would take the chance on the streets.
one non-french driver to consider, Riccardo Patrese. extremely talented and pushed every part of life to the extreme. he was an italian driver with a flare for the dramatic.
by the way, in 1978 a few americans ventured around the F1 tour. you may have heard of some of them, Mario Andretti(1978 World Champion and member of Philly Region of the SCCA since the mid-60's), Eddie Cheever who has won in jsut about every form of sports cars in north america, and some 25 year old upstart named Bobby Rahal made 2 starts during the 1978 season, he went on to run pretty well at a place called Indy over the next few decades
