^Completely different rides IMO. Kanonen's main feature is the launch, whereas on Helix it serves the purpose of a moderate thrill instead of a lift hill. Not once did I compare the rides during my day at Liseberg.
To wade in on the Kanonen argument, I'd put it as follows on the Accelerators scale;
Top Thrill Dragster
Stormrunner
Furius Baco
Stealth
Kanonen
Kingda Ka
Desert Race
Rita
I think it's pretty damn good to be fair, easily the 3rd best coaster in the park.