While it is uncertain that the heroes from the Marvel Netflix shows would show up, these are the heroes that are most likely to appear in the 2017 reboot
Captain America
Iron Man
Black Widow
Scarlet Witch
Falcon
Hawkeye
War Machine
The Vision
Dr. Strange
and Ant Man
As far as most people can guess on the number of Avengers appearing, some of them might just cameo either during, at the end, or in the post screen credits of the film, but then again, their appearances in the film might expand from cameos to longer and normal appearances if they get involved with Spider-Man's battle against the villains he will be facing in the movie like the Sinister Six, featuring 6 of the wallcrawler's most popular enemies and perhaps 1 additional villain that will bring them out into terrorizing the city but other than how unclear on who is sure to make it through Captain America Civil War alive that with actor Don Cheadle confirming that the movie will have a lot of people killed there is a slight chance that the Russo Brother's have a big surprise in store for us after the brawl between heroes in this film ends. Well we can find out once production and filming gets underway later this year