I remember when I was a kid involved in Cub and Boy Scouts we used to have annual rocket launches as part of our pack/troop. My sons are a few years away yet from scouting, but my brother has 3 son's all involved right now and is interested in starting a similar annual event with their packs/troops, and was curious if they could get involved within CMASS. Is there someone specific within CMASS they should reach out to to?
I won't speak for CMASS, but RIMRA works with scout groups at least once per year. It's a little bit of a drive to Kingston, but we can help if you don't have any other options.
Over the years that I have been with CMASS we have had Cub Scouts show up on many occasions, although I do not recall any Scouts. This appeared to me to be on an ad-hoc basis. That is, the Scouts chose a launch to attend and showed up. That said, they did give us advance warning, so we knew to expect them. If you want to make a more formal arrangement, what that might look like could be a topic of discussion at a club meeting.