iMac 27" 5K i7 2017 starts to blow like h**l when Chrome Canary is open with just 1 tab
I resolved this issue by doing the following:

I checked my Wi-Fi and Ethernet connexions to spot if there was a problem there and I noticed that there where more than 5.000 mach thingys active and the number kept on growing on the Ethernet connexion.
I first thought that it was some kind of DDos attack...  

To be sure, I reset my switch.
Once the switch was back up, the problem was resolved.
Now the 'SystemUIserver' is running at 0.1% and this with like 10 tabs open in Canary.