He might be able to apply for a 10-year visa in the near future for his mum though; keep that in mind.....
As far as I am aware, Canada does not issue 10year visa's, that is the USA.
6 month visitor visa's maximum. Renewal is up to the IO getting the request, there are no guarantee's that the visa will even be extended once, especially if immigration suspect that the 'visitor' is really living in Canada.
Truth is, Canada is getting more reluctant to even issue the first visitor visa's to parents now. Get the first visa, then start thinking about what to do after 6 months.