The filter size for the Canon 35mm F2 is 40mm. Canon Slimline (original RF filters) are your best bet. I own a UV and G1. Recently I picked up a couple of 40mm Walz German filters (Y1 and Blue), for the Canon RF, but I haven't finished fully testing those. All of the generic hoods and filters I tested caused barrel vignetting (to some degree), F22 is the most critical test, when focused at infinity.
Original Canon Slimlines are tough to find, but not impossible to get. They do turn up, I have found in my experience. I dropped out of an Ebay auction recently, for a Y1 40mm Canon Slimline, at $58! Then I got the Walz Y1 for $1.99 and the dealer threw in the Blue one.
The Canon lenscap can be black plastic, or chrome, depending on the vintage. Either will work, I prefer the chrome, myself. 42mm Canon is what you want.