Well pressure within a sealed container is defined by the
pressure surrounding the container. If the pressure outside is
equal to the pressure within the sealed container, there is no
positive or negative pressure gradient. If the pressure outside is
less than the pressure within the sealed container, there is
positive pressure increase within the container.
Because air in the higher atmosphere is of lesser pressure than
at ground level, bringing a seal container filled at ground level
to the higher atmosphere will cause the sealed container to
increase in internal pressure. However, you asked what will
happened within a pressurized airplane, pressurization within the
airplane is meant to prevent the pressure within the cabin from
dropping to that of the surrounding environmental pressure.
Therefore a sealed container within a pressurized airplane should
not change significantly, assuming the container was filled at
ground pressure, the pressure which cabins are pressurized to.
