Good cans that still have all the packing in them should be no warmer than what your hand can take, at a steady power level consistent with touring that is.
SS cans run the hottest.
Then titanium, as in a bit cooler.
Then CF, being the coolest.
Regardless of can material, skin temp goes up as the packing degrades and/or the steady state power level goes up.
At least some bags are designed for laying against cans, having a more heat resistant material on the resting surface.
One can also put some exhaust wrap on the cans where the soft luggage rests.