Both are great riggers, I’ve owned and ran them both.
I prefer the Scotty HP’s myself for a few reasons, but mainly because they are a lot faster than the Cannons which is nice if you’re fishing 100’+ with 15# plus balls.
The tip-up booms are nice feature with them too.
My only gripe about Scottys is the end roller on the boom can ice up and jam the beads for the autostop in really cold temps.
Whatever riggers you end up getting, I highly recommend buying ball snubbers to help take some of the shock off of everything, especially with Cannons for how quick they come to a stop.
Scotty parts are harder to come by locally, but their service and Lifetime Warranty is outstanding.
This spring I had a buddy trip/slip and break a rod holder right off the rigger by falling on it.
After a quick call to Scotty they sent a free replacement under the lifetime warranty even though it was an accidental incident.