For PhD students, please include details on your research interests/plan/background. It is important that your interests mesh with mine, so be clear on how your research goals would fit within my areas of interest.
For MSc students, you do not necessarily need to contact me first or propose any particular research goal. I would be happy to be notified of your interest, and I would be happy to talk to you in person once you are admitted.
Here is a link to general admission information for students interested in studying Computer Science or Software Engineering at McGill University.