How much time you need to prepare for the SAT depends on what exactly you're rusty in. If you're just feeling like you need to re-familiarize yourself with standardized testing and the test format, your time commitment may not be that high - potentially fewer than 40 hours. On the other hand, if you really need to teach (or re-teach) yourself some of the subject matter, like geometry, you could potentially invest hundreds (if not thousands) of hours in the test.
To figure out how long you'll need to prepare, you need to sit down and take a realistic practice test. This means timed conditions, no extra breaks, no distractions. Once you've done that, you'll get a better sense of where you are (compared to where you need to be). You'll probably find our guides on how long to study for the SAT and how early you should start preparing for the SAT helpful in your studying.
But do you even need to take the SAT as a student who's already attended university in Canada? It really depends on what schools you're applying to. For example, the University of Minnesota requires only those transfer applicants who have fewer than 26 transferable credits to supply an SAT or ACT score. The University of Washington, on the other hand, doesn't require SAT or ACT scores for any international students (transfer or not). In order to know if you actually need to take the SAT, you'll need to research the admissions policies for transfer students at each school you're considering applying to.
Here is a list of three other American colleges and universities with a brief description of their transfer policies for older students finishing their degrees:
NYU: No standardized tests required if you've completed at least one year of full-time college/university enrollment - otherwise, you have to complete the same requirements as any freshman applicant. TOEFL required in some cases for international non-native English speakers. You'll also need your college transcript (strong applicants usually have at least 32 credit hours) and any other requirements for the particular program you're applying to.
- Washington University in St. Louis, University College: No standardized tests required; applicants must have a high school diploma and a GPA of 2.7 or better for a certain number of units of college-level course work (the number changes depending on the program). TOEFL not required for Canadian citizens.
- Wellesley College, Davis Degree Program: No standardized tests required; applicants must submit an official high school transcript and/or GED scores, an official college transcript for the courses you've completed, an evaluation from college instructors (or employer or volunteer activity supervisor, if you've been out of college too long), and an updated resume.