It is good to read through the list of Roadtreks for sale on the Roadtrek Chapter site: http://www.roadtrekchapter.org/roadtreks-for-sale
You can read what has been replaced or what the owner thinks needs to be replaced on the older units. It gives you a good idea idea of US pricing but, as you've probably have seen, prices tend to be a bit higher in Canada.
222,000kms = 138,000 miles. It is high but not that bad. All the usually items should be checked out so your comment that you'd get it mechanically inspected is smart.
The brakes might have been replaced because of use or not being used. I'd prefer that it was from use and not from sitting and getting rusty. Definitely inspect the underside for rust. I've bought a few rusty vehicles over the years but won't ever again.
Tires can be a big expense. Go by age first, then tread. Many RV'ers won't run tires over 6 years old. These vans typically run near max weight so tires are important.
Yes, it would be nice to have something newer but brand name Class B Vans don't get much cheaper than the price you quoted. Assuming it is good shape for its 23 year old age then you should get a few years of enjoyment and still be able to sell it fairly quickly if camping this way no longer interests your family.
Buyers often ask if the RV has a generator and an air conditioner- those two items help with resale. Also, check to see if it has a water heater. Things like that are expected these days but were options back then.