Ok, this happened to me last year (and it's very annoying the way they don't tell you things)
You (or somone you nominate) must be here in January to sign the UAC form confirming your choice of course. If you plan to have somone else do it you need to fill out a special form and send it to UAC (form should be in UAC guide or online).
If you are away for the acceptance of your course, then you must be back for enrollment. Dates for this should be on indivdual uni's websites ...