I do not think you need to prove that you would be revisiting again.
You have to satisfy the visa officer (VO) that you would be returning to UK (job, bank statements, house lease ...). It does not matter in this case whether you apply for single-entry or multiple-entry as you would be returning to UK.
You can apply for the multiple-entry visa. Make sure to include all the documentation (
http://www.canadainternational.gc.ca/united_kingdom-royaume_uni/visas/visit_eligible_visite.aspx?lang=eng).