If you may be interested in obtaining your Public Accounting Licence in the future, you are required to complete the Taxation and Assurance elective modules. If this does not apply to you, you should consider your work experience, interests, and comfort level with each elective area based on your past educational experience to determine which electives would be most suitable for you.
CPA Canada has posted sample cases for each of the Electives here. You can also read through the sample cases and evaluation guides (solutions) for each module to help inform your decision.