Note: Unfortunately, due to email overload, I can only reply selectively, but don't let this discourage you from emailing me. I do read all email.
Graduate Students
We take students from the incoming streams of accepted students from the Molecular Genetics or Computer Science departments. Please see those websites for information about applying. We regularly take students, but can't reserve spots until after students are accepted into a graduate program.
Undergraduate Research Students
Undergraduate students seeking a Computational Biology/Bioinformatics research position are encouraged to contact Gary Bader by e-mail. There are various opportunities like summer research programs (e.g. DSI SUDS), and project courses e.g. BCB430 that can be taken during the school year or over the summer. Strong computer programming ability and biology interest are required.
UpbeaT, the Student Life blog for the UofT St. George campus has a useful post with advice about summer positions: http://blogs.studentlife.utoronto.ca/UpbeaT/2009/11/06/so-you-want-a-summer-research-position/
Post-Doctoral Fellows
We periodically have excellent research opportunities for Post-doctoral fellows. Please email your CV and a statement of research interests to Gary Bader.