The provisional 21-race 2017 Formula One calendar has been unveiled with the German, Canadian and Brazilian grands prix still listed as subject to confirmation.

While Australia will again host the season opener in Melbourne on March 26, a week later than this year's race, there is less certainty about a number of other races.

Germany remains uncertain due to Hockenheim's stated reluctance to host a grand prix every year while Formula One's 85-year-old commercial supremo Bernie Ecclestone has been pushing for improvements to the Montreal circuit and the Interlagos track in Sao Paulo.