At least 508 soldiers: the number given in the text are for three units only.
For example, the text gives the number of 156 British Engineers killed in the raid: 200 British soldiers are buried in Rennes with a death date on 17 june 1940, including some RAF ones, for example.
See a list there for 177 of them :
http://www.lelancastria.com/17-juin-...-Rennes-a.html
The body count of this raid will probably never be known: the first link I gave said that 805 bodies were buried, and speculates that around one thousand people were killed by the bombing and the explosion (including civilians), but all other sources will give numbers between 2000 and 5000 dead... but without any more details.