Last time C/B were at SC, they were seeded 3rd so basically had no choice. I'm sure they would have preferred not to compete against V/M in their comeback season but the top 2 seeds didn't either, so... And V/M won, so it probably went over well for SC and the audience.
In normal times, it would probably be better for C/B to go to China and Russia (no P/C, likely at least 2nd, barring disaster) but with YKW and the less effective Chinese and Russian vaccines, Delta variant and who knows what else by then, I hope they don't go there. P/C will be in France and likely at NHK, so it seems like the best/safest option for C/B is SA and SC. We'll see what happens.
In terms of other teams, S/K will likely want China as their 2nd event so both H/D and G/P will need to compete against P/C. And yes, I assume G/F will be at P/C's events.