I remember a few years back their was a couple who spent the entire summer canoeing the Quetico and BWCA.  I remember reading an account, (In the Ely Echo or Duluth News) that said they saw very few people in the heart of the canoe country.  On one occasion late one afternoon, twilight, a solo canoeist came up to their campsite and asked if he could camp with them.  They declined the offer, for privacy reasons, but later they felt remorseful.  I probably would of felt the same way, unless I had built some repore with the person.  

We always strike up a conversation with anyone we see on a portage or who happens to canoe by our campsite.  If we were eating lunch, we have even offered to share available food if we had extra.  If we had anything in common, we also would welcome them to stop by our campsite.  But I'd probably decline camping with an unknown person unless they needed assistance.