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I attended the citizenship ceremony yesterday which swore in 30 new Canadians, here's rough break of the attire:
Approximately 30% people were in fully formal attire, 30% wore semi formal, 20% wore smart/business casuals, 15% wore traditional/religious attire, 5% wore casual attire!!! I was in a semi formal attire...
 
Well, we would have to agree on what you mean by "fully formal" (https://en.wikipedia.org/wiki/Formal_wear). I've attended three citizenship ceremonies and didn't see anyone dressed in a tuxedo/ball gown. Otherwise, yes, there were people who were well dressed (suits/sport coats) and people who didn't seem to care how they were dressed (jeans/hoodies).