It's an interesting point of law, isn't it? In the case of the B&B the two men were clearly discriminated against.
In this case, in a province where gay marriage is not possible, and where it was a particular transaction that was declined, it may be different.
Imagine a scenario where a baker was asked to include a slogan saying 'Lower the age of consent to 14'. That would be campaigning for a change in the law which many would disagree with. Should the baker be allowed to refuse to make this?
Or perhaps 'Abortion on demand up to 30 weeks'. Against the law as it stands but some would support this position.
The question is, which takes priority: freedom to compel a service provider to participate (however tangentially) in a campaign, or the freedom to refuse.
As I said above, it will have to be tested in the courts if it ever gets that far.