You are correct that in normal operations most aircraft have the cabin slightly lower than the outside during landing. There are situations where we turn the bleeds off, this has the effect of giving us slightly more power from the engines in case we need it for go-arounds. An example would be for some types taking a tail wind of more than 10 knts.
The reason why they do this is because the additional pressure has a stiffening effect on the hull which leads to a decrease in engineering stress on the structure which leads to less fatigue history. Think empty plastic bottle that's closed that gets heated in the sun.
If the cabin pressure stays the same as at attitude the cabin will be less pressure than outside. There is a safety valve which allows air into the aircraft to balance things out so the hull doesn't crush like a plastic bottle if you suck the air out.
If by some bizarre combination of events you get on the ground with negative pressure internally there is a possibility of the doors being pushed in when opened but as they all swing out by some method there is a mechanical stop to stop them getting blow in the way.
The only way I could imagine a door being opened with the internal pressure being more than the outside would be when someone opens the doors with an engine running and other system failures present. The doors are approximately 2 meters square. anything more than 300N force required to open (ie lift 30kg) is going to mean that the person opening is going to know there is something different to usual. over the door that equates to 150N/m2 which is 0.0015 Bar or 0.002PSI where bar is standard atmosphere. So even the slightest pressurisation means the door is solid.
In cruise at FL 350 the cabin is pressurised to 8000ft which is 0.75 bar. Outside pressure is 0.24 bar giving 0.51bar differential which over 2m2 equates to 102 tons of force required to move the door.