Of course just closing borders and calling it a day is ineffective, but it would have helped in slowing and mitigating the spread. I recall a lot of acrimony around this topic back in March and talking down to people who thought it may have been a good idea to do so (closer borders). Given the infected count exploded in mid-march, it infections likely started in early march/late February, either from unaware carriers who left China, Chinese travellers outside Wuhan who entered Canada normally, other travellers who may have had contact with infected people from China, or from international travellers who weren't careful during their voluntary self-isolation or didn't bother to do so at all (mandatory self isolation wasn't even a thing until late March)

And coming from Canada's top doctor here, it's much harder to argue this as ineffectual. We've been told to trust the medical team in charge afterall.