In my head, I wrote that the Cross-Flow with the SunSun is for my 75g SW. Guess I didn't actually type it out. Oops! Sorry lol.Well, I do not know the gph rating on your SunSun. However, if it's a 304b or similar, I would advise against using 3/4 pvc as they'll be too big to get adequate flow into the tank. Try to stay as close to possible as whatever the ID is of the stock tubing. As for the canister + wave maker on a 125, I believe you'll be fine.
We're going to do something like what you did for your FX on our Fluval 406 that's running on the 125. The outflow from that filter is way too fast. It'll actually push our plants horizontal.