The pressure inside a can of soda is around 2 to 3 atmospheres (above ambient i.e. 3 - 4 atmospheres total) depending on who you believe. The solubility of CO$_2$ increases with pressure, so when you open the can the pressure immediately drops by 2 - 3 atmospheres, i.e. by a factor of 3 to 4. As a result the solubility of the CO$_2$ decreases and the excess CO$_2$ comes rapidly out of solution as gas bubbles.
In the underwater station at 2.5 atm the pressure difference is only 0.5 - 1.5 atmospheres, so when you open the can the pressure decreases by a much smaller amount i.e. by a factor of only 17% to 33% compared to a factor of 2 to 3 at surface pressures. Accordingly the solubility of the CO$_2$ decreases by a much smaller amount. Excess gas will come out, but much less and much more slowly.
If you went a bit lower in the sea and raised the ambient pressure to above 3 - 4 atmospheres the soda would actually absorb gas when you opened it.