That is an interesting way to twist the issue, and I would not be surprised if it was presented that way in Canadian news media, but as far as I know, the baker was willing to provide the couple a cake, just not a cake decorated in a male-male wedding theme, and the couple did not want any of the cakes the baker was willing to bake and decorate.

Put another way, the baker's objection was not to providing the male-male couple any cake, but to decorating a cake as they had requested. The baker would presumably have been willing to provide a "regular" wedding cake, decorated as if for a male-female couple, or perhaps even a "generic" wedding cake, with no mention of the sexes involved, but those are different products from a cake decorated with a male-male theme.

This is not sex discrimination, but rather the freedom of a business to determine what products they will carry with extra sides of implication against freedom of religion in that the product the business chose not to offer for sale happens to conflict with the business owner's religious beliefs and freedom of expression in that the baker, in decorating cakes, is in the business of producing art. Both freedom of religion and freedom of expression, including willful non-expression (which is itself a type of expression) are Constitutionally protected here in the United States.

Our 5th Amendment famously provides a right to remain silent in the context of a criminal investigation, but our 1st Amendment also provides a right to remain silent whenever you want. The refusal to speak can itself be seen as a form of (protected) speech.

The Supreme Court decision you cited was in a case concerning employment law, which is not applicable to the example of a bakery declining to produce a particular custom-decorated cake. The Supreme Court has generally held compelled speech to be quite odious.