Obviously all of the information on a person's income tax and benefit return...so that would be the SIN, their income, and the credits they're applying for. To apply for some credits, you need to provide additional information. It could be medical information, if you're applying for a disability tax credit, for example.
For businesses, the general approach is the same. They must obviously provide business income. They must provide information on the GST and HST that they have collected on behalf of the government. If they are applying for credits, for example, business credits like the research and experimental review credit, they will have to provide information on the work they're doing in order to qualify for that credit.
It's very hard to summarize it in a way that's concise, but yes, we collect a significant amount of information. That's really only a taste of it.