The size of the Christmas bonuses this year depends on whether the sales department can open the market in Southeast Asia.
The size of the Christmas bonuses this year depends on the possibility that the sales department can open the market in Southeast Asia.
The size of the Christmas bonuses this year depends on whether the sales department can open the market in Southeast Asia.
The size of the Christmas bonuses this year depends on the possibility that the sales department can open the market in Southeast Asia.
The idiom "depends on whether" is correct, and the structure "depends on the possibility that" is unnecessarily wordy.