No, you've got that mixed-up.  We don't assess 'reasonable limits' when determining what constitutes a sincere religious belief.  Religion isn't based on reason. Reasonable limits enter into it when considering the application of religious beliefs.

And it doesn't matter if the majority of muslims don't agree; both religion and sincerity are personal things.  As the SCC wrote, it's "irrespective of whether a particular practice or belief is required by official religious dogma or is in conformity with the position of religious officials."  

Cross-examination is only required if there are grounds to believe someone's faking it - as was the case with the only legal dedision about "pastafarians" I've been able to find.  The decision said their claims were a mockery and did not qualify as religious beliefs.