Is there a certain time of year that Canadian Universities make graduate admissions offers?
It's not uniform, and the lack of uniformity basically makes it a race: it is not uncommon for offers to have a very short window to accept, in the hope of recruiting (some would say trapping) good candidates early on.

It is not impolite to ask for updates or timelines.  

It is often the case that faculty must commit some grant monies for student support, and Canadian grants are usually smaller than in the US.  As a result, unless you have a generous scholarship, the system is more dependent on individual "matchmaking", i.e. finding a suitable supervisor willing to poney up the funds, rather than acceptance on pure academic record, although the wealthier and/or larger programs will accept students "at large" without firm supervisory commitments.  

If you require funding but none of prospective supervisors has funds left, nobody will be in a hurry to make you an offer. If you have an offer, the better option is to contact these prospective supervisors directly, explain that you have an offer, and hope someone can give you a quick answer.