Each justice of the Supreme Court of Canada has three law clerks. This number has been as high as four in the past. There is also support from library staff, jurilinguists, translators, and editors.
At provincial courts of appeal, the support from law clerks and other legal staff (court counsel, research lawyers, librarians, and assistants) varies depending on province. See Melanie Bueckert, "Legal Research in Canada's Provincial Appellate Courts" (2011). In 2011, the highest amount of support was in Quebec (26 clerks, 8 research lawyers, for 25 judges). The lowest was in Prince Edward Island, with no clerks or researchers for three judges.
The Federal Court and Federal Court of Appeal judges each have one clerk each.
At the Tax Court of Canada, the pool of clerks is available to be assigned work from any of the judges of the Tax Court.
There are also clerkship programs at several provincial superior courts, but there, the clerks are assisting many judges. There are also research lawyers and library staff.
At lower level statutory provincial courts, there is almost no support other than a couple court-wide research lawyers and library staff, or sometimes short, unpaid, for-credit internships as part of a law degree.
How any judge uses the resources at their disposal is confidential, but some public information is available in Melanie Bueckert's article above (for provincial appellate courts), and in some articles about the Supreme Court of Canada clerkship program (e.g. Mitchell McInnes, Janet Bolton & Natalie Derzko, "Clerking at the Supreme Court of Canada" (1994)).