Kenmore canister vacuum has no suction?

While it's possible that a bag can get so full that it actually cuts down the suction on a modern cannister vac, it's highly unlikely. A far more likely possibility is that there's an obstruction in the flex hose that goes down to the power head, or in the neck of the power head itself. Check those two places and you'll likely find the problem. You can test this by removing the hose from the tank and restarting the machine. If there's good vacuum at the tank, then it's certainly in the hose or power head.