I looked into this a bit more and actually no, I don't think it's within the limits of the law. Pattison Outdoor is a marketing/advertising company, and the B.C. Human Rights Code prohibits discrimination without a "bona fide and reasonable justification" in providing services available to the public on the basis of many different things including religious (or non-religious) beliefs. Pattison has shown that as a business it does not steer clear from controversial ads. They previously created a billboard for Signs for Life that featured the head of fetus with text that wrote: “Abortion: aren’t we forgetting someone?” Clear discrimination is present here.