We know this because he posted the following tweet confirming as much just minutes ago:
Ok @StardustWWE -- you asked for it. See you next Monday. #AmellGetsRaw pic.twitter.com/A9v9ReZHa5— Stephen Amell (@amellywood) August 4, 2015
This comes after various rumors that Amell may show up at Monday Night Raw next week in Everett, Washington because he's in the area. The question now is whether or not he'll show up as Stephen Amell or as "The Green Arrow." The photo sure makes it seem as though the latter will be true.
Either way, we can finally look forward to something actually happening instead of talk that it might.